What Is Systemic Risk Today?*Oliver De Bandt
European Central Bank

Philipp Hartmann
European Central Bank

Abstract
This paper develops a broad concept of systemic risk, the basic economic concept
for the understanding of financial crises. It is claimed that any such concept must
integrate systemic events in banking and financial markets as well as in therelated payment and settlement systems. At the heart of systemic risk are contagion effects, various forms of external effects. The concept also includes financial
instabilities in response to aggregate shocks. The quantitative literature studying
systemic risk is surveyed in the light of this concept. Rigorous theoretical modelsof contagion have only started to be developed, so that a sound theoretical basisof the notion of systemic risk is still lacking. Econometric tests of contagion
effects seem to be mainly limited to the United States regarding banking markets,to international spill-over effects during the 1987 stock market crash and tocontagious currency crises. Geographical coverage as well as coverage of financial markets and their settlement systems appear to be very incomplete. Moreover,the literature surveyed reflects the general difficulty of developing tests that canmake a clear distinction between rational revisions of depositor or investor expectations (“information-based” contagion) and “pure” contagion. It is concluded
that, given the importance of systemic risk for the understanding of financial
crises and for policies to ensure the stability of financial systems, it would bedesirable if additional research could fill the gaps identified.

*
The authors wish to thank, without implication, Lorenzo Bini-Smaghi, Frank Browne, Pietro
Catte, E.P. Davis, Mark Flannery, Charles Goodhart, Mauro Grande, Tim Montgomery, María Nieto,
Daniela Russo, Benjamin Sahel and the participants of the ECB Research Seminar and of the
Banking Supervisory Sub-Committee Meeting in Brussels for their comments on an earlier draft ofthe paper. Any views expressed in this paper are the authors’ own and do not necessarily reflect
those of the European Central Bank.
Both European Central Bank, DG Research. Correspondence: Olivier De Bandt / Philipp
Hartmann, European Central Bank, DG Research, Kaiserstrasse 29, 60311 Frankfurt, Germany.

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1

Oliver De Bandt and Philipp Hartmann

Introduction

There is under way a significant rise in concerns about the stability of national
and international financial systems. These concerns are reflected in a series ofrecent official summits and reports, private initiatives and academic papers,1 andthey have been underlined by the on-going East-Asian crisis, the Russian crisisand now also the Brazilian crisis. Fears exist that such developments may spillover to even more countries. Although the increase in theoretical, empirical andpolicy analyses of financial instability has been substantial, practically all writings share—in our view—the following limitation: while “systemic risk” is now
widely accepted as the fundamental underlying concept for the study of financial
instability and possible policy responses, most work so far tackles one or several
aspects of that risk, and there is no clear understanding of the overall concept ofsystemic risk and the linkages between its different facets.
In this paper we attempt to set a starting point for a more comprehensive
analysis of systemic risk as the primary ingredient to understand financial crises
and as the main rationale for financial regulation, prudential supervision andcrisis management. In the first step we bring together the most important elementsof systemic risk and integrate them into a coherent working concept, which could
be used as a base line for monetary and prudential policy decisions to preserve thestability of financial systems. While the “special” character of banks plays amajor role, we stress that systemic risk goes beyond the traditional view of single
banks’ vulnerability to depositor runs. At the heart of the concept is the notion of“contagion,” a particularly strong propagation of failures from one institution,market or system to another. Especially nowadays the way in which large-value
payment and securities settlement systems are set up as well as the behaviour ofasset prices in increasingly larger financial markets can play an important role in
the way shocks may propagate through the financial system. While in thepresence of rapidly evolving financial institutions and markets and the particularcharacteristics of each financial crisis it might be futile to look for a single, ultimate definition of systemic risk, it may still be useful to give some general structure to our thinking in this area in order to help avoiding piece-meal policy making.
In the second step we review the existing theoretical and empirical literature
about systemic risk in the light of the overall concept developed before, in order1
Financial stability issues have recently been addressed at the G-7 1995 Halifax, 1996 Lyon and1997 Denver summits. Among the reports and papers are Committee on Payments and Settlements
Systems (1996), Federal Reserve Bank of Kansas City (1998), Goodhart et al. (1998), Group of
Thirty (1997), International Organization of Securities Commissions (1998), Lindgren et al. (1996),
Peek and Rosengren (1997), and Working Party on Financial Stability in Emerging Markets (1997).
By the time of this paper's last revision, the world was also awaiting a report by Bundesbank
President Hans Tietmeyer on whether and how the international financial architecture could bereformed to better withstand situations of crisis.

What is systemic risk today?

39

to identify areas in which future research efforts are needed. More specifically,
the survey of the empirical evidence on systemic effects, in particular on contagion effects, endeavours to clarify the practical relevance of several risk elements
identified in the conceptual part. We focus primarily on the quantitative literaturein this area. This should not be interpreted as meaning that we consider the more
descriptive literature of particular crisis periods in history as not being important.
This choice has rather been taken, first, to limit the amount of information to be
surveyed to that which can be dealt with within a single paper and, second, tofocus on analyses for formulating and testing very specific hypotheses with themost advanced techniques.2
The somewhat unusual procedure to proceed from the general concept to asurvey of the current literature is motivated by the fact, that—from prior reading—this literature appears to be very incomplete, when one confronts it with theissues raised by actual crisis situations. In this sense we try to set out, first, what
we think is important for the understanding of systemic risk and, second, study
where—in our view—satisfying answers have been given and where not. Considerable gaps are identified. First, there do not yet seem to be models which canprovide a sound theoretical basis for contagion, neither in banking markets, nor in
financial markets nor in payment and settlement systems. Models linking all thethree areas are simply non-existent. Second, the overwhelming part ofeconometric tests for contagion effects is limited to data for the United States.
Event studies of bank equity returns, debt risk premia, deposit flows or physicalexposures for European or Japanese data are rare or virtually absent. Similarly,
while there are numerous studies about the correlations of asset prices in general,
the evidence about cases where one financial market crash causes another market
crash is much more limited. Where those securities market contagion studies exist,
they mainly look at contagion within the same asset class without looking at
potential contagion (or at “flight to quality”) with other asset classes. For bothbanking and financial markets it appears to be hard to disentangle “rational,”
information-based revisions of expectations from “pure” contagion. Finally, mostquantitative analyses of contagion effects in payment systems seem to be limited
to net payment systems, widely ignoring securities settlement systems or “network externalities” potentially resulting from “gridlock” situations in real-timegross payment systems.
We very much hope that our paper will help stimulate further research efforts
aiming at filling the gaps identified as quickly as possible. This should provide
important conceptual inputs for the understanding of concrete examples of finan2
The only other large literature surveys in the area of systemic risk we are aware of have been
written by Kaufman (1994) and Davis (1995). However, the former is narrower in scope than ours,
focusing on bank contagion alone, mainly but not exclusively taking an empirical perspective. The
latter is broader than this, but it does not consider the latest developments nor interpret the earlier
literature within one coherent concept of systemic risk. Freixas and Rochet (1997, chapter 7) give athorough theoretical exhibition of a selection of key models in the bank run literature. Dowd (1992)
reviews this literature critically. Masson (1998) provides a short survey in the area of contagious
currency crises (see section 3.2.1.).

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Oliver De Bandt and Philipp Hartmanncial crises and for potential policies to prevent or alleviate future crises. However,undertaking this research or giving any policy advice is beyond our present scope.
The remainder of the paper is organised as follows. Section 2 contains thegeneral conceptual discussion. It provides the framework within which the theoretical and empirical literature will be interpreted in the following parts. Section 3
gives a detailed account of systemic risks in banking markets, financial markets
and payment and settlement systems, surveying theoretical models explaining
them and adding theoretical considerations where no model is available. Section 4
surveys a large number of econometric tests and some other quantitative assessments of the various facets of systemic risk described before. Section 5 concludes.

2

The concept of systemic risk

Systemic risk in a very general sense is in no way a phenomenon limited toeconomics or the financial system. Maybe the most natural illustration of theconcept is possible in the area of health and epidemic diseases. In severe cases(e.g. the Great Plague in the Middle Ages) widespread contamination with adisease may wipe out a significant portion of a population. In the area of
economics it has been argued that systemic risk is a particular feature of financial
systems. While contamination effects may also occur in other sectors of theeconomy, the likelihood and severity in financial systems is often regarded asconsiderably higher. A full systemic crisis in the financial system may then havestrong adverse consequences for the real economy and general economic welfare.
The objective of this section is to provide a general framework for the
economic analysis of systemic risk. We start out by proposing a specific terminology, clarifying some general elements of the concept of systemic risk andleading to a general working definition of it. Then, the main arguments are discussed as to why financial systems can be regarded as more vulnerable to systemic risk than other parts of economic systems. Since information asymmetries
can play a crucial role we proceed in the next section by distinguishing between
self-fulfilling systemic events and those that can be regarded as individually
rational responses to the revelation of new information between agents. Finally,
the relevance of systemic risk for public policy is briefly examined.

2.1

Systemic events

In order to reach a definition of systemic risk in financial systems, we first clarify
a number of concepts—illustrated in Table 1—needed for that definition. We
define a systemic event in the narrow sense as an event, where the release of “badnews” about a financial institution, or even its failure, or the crash of a financial
market leads to considerable adverse effects on one or several other financial
institutions or markets, e.g. their failure or crash. Essential is the “domino effect”

What is systemic risk today?

41

from one institution to another or from one market to another.3 Systemic events inthe broad sense include not only the events described above but also severe andwidespread (“systematic”) shocks which adversely affect a large number offinancial institutions or markets at the same time. A systemic event in the narrow
sense is strong, if the institution(s) affected in the second round or later actually
fail as a consequence of the initial shock, although they have been fundamentally
solvent ex ante, or if the market(s) affected in later rounds also crash and would
not have done so without the initial shock.4 (Otherwise, i.e. if the external effect isless than a failure or a crash, we denote a systemic event in the narrow sense as
weak.) Similarly, systemic events related to systematic shocks are strong (weak),if a significant part of the financial institutions simultaneously affected by them
(do not) actually fail.
Based on this terminology a systemic crisis (in the narrow and broad sense)
can be defined as a systemic event that affects a considerable number of financial
institutions or markets in a strong sense, thereby severely impairing the general
well-functioning (of an important part) of the financial system. The wellfunctioning of the financial system relates to the effectiveness and efficiency withwhich savings are channelled into the real investments promising the highest
returns. For example, a systemic financial crisis can lead to extreme credit rationing of the real sector (“credit crunch”).5
Systemic risk (in the narrow and broad sense) can then be defined as the riskof experiencing systemic events in the strong sense.6 In principle, the spectrum ofsystemic risk ranges from the second-round effect on a single institution or market (column “single systemic event” in Table 1) to the risk of having a systemiccrisis affecting most of the (or even the whole) financial system at the upper
extreme (column “wide systemic event” in Table 1).7 The geographical reach ofsystemic risk can be regional, national or international.

3
Notice that such systemic events do not include the failure of a single financial institution as aconsequence of a wild decline of some asset value.
4
A market crash can be defined as an unusually large general price fall. In statistical terms thisfall can be made more precise by relating it to the extreme percentiles of the respective market’s
empirical return distribution. E.g. cases where a representative price index decreases by a higher
percentage than the 1 or 5 percentile of the historical return distribution (i.e. the left tail of the
distribution) could be defined as crashes.
5
Other accompanying factors of a systemic crisis may include severe liquidity shortages invarious markets, major inefficiencies in the allocation of risks and severe misalignments of asset
prices.
6Bartholomew and Whalen (1995) as well as Goldstein (1995) review various definitions ofsystemic risk. We think that our definition can “nest” most other definitions used so far. See also
Aglietta and Moutot (1993) and Davis (1995).
7
However, as pointed out by Kaufman (1988), due to “flight to quality” it is unlikely in practicethat, for example, all banks of a country face a deposit run at the same time. A similar point will
apply to financial market crashes.

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Table 1: Systemic events in the financial system
Type of initialshock

Narrow shockthat propagates· Idiosyncratic
shock· Limitedsystematicshock
Wide systematic
shock

Single systemic events (affect only
one institution or one market in
the second round effect)

Wide systemic events (affect many
institutions or markets in thesecond round effect)

Weak (no failure Strong (failure
or crash)of one institution or crash of
one market)

Weak (no failure Strong (failures
or crash)of many institutions or crashesof many markets)

4

4contagion

4

44contagion

4

44contagion
leading to asystemic crisis
4contagion
leading to asystemic crisis
4systemic crisis

The key element in this definition of systemic risk, the systemic event, iscomposed of two important elements itself, shocks and propagation mechanisms.
Following the terminology of financial theory, shocks can be idiosyncratic or
systematic. In an extreme sense idiosyncratic shocks are those which, initially,affect only the health of a single financial institution or only the price of a single
asset, while systematic (or widespread) shocks—in the extreme—affect the whole
economy, e.g. all financial institutions together at the same time.8 An example ofan idiosyncratic shock to a national financial system is the failure of a single
regional bank due to internal fraud. The sudden devaluation of a noninternationalised currency due to an unsustainable domestic budget deficit can be
regarded as an idiosyncratic shock to the world financial system. Examples ofsystematic shocks to national financial systems are general business cycle fluctuations or a sudden increase in the inflation rate. A stock market crash in itself
acts as a systematic shock on most financial institutions. The same applies to aliquidity shortage in an important financial market, which can be related to acrash or to some other event throwing doubt on the financial health of counterparties usually trading in this market.
8
Since it is widely used in finance, we prefer the term “systematic” for wide shocks. Whereas asystematic shock implies a systemic event, as explained above, a systemic event does not need tooriginate in a systematic shock. Therefore, the two terms have to be distinguished.

What is systemic risk today?

43

Of course, there is a continuum of intermediate types of shocks (e.g. sectorwide or regional) between the theoretical extremes of idiosyncratic and wide
systematic shocks. It is important to note that idiosyncratic shocks that do not
propagate widely are “insurable,” in the sense that an investor can protect herself
against them via diversification, whereas wide systematic shocks are “uninsurable” or non-diversifiable. Negative systematic shocks, such as a severe recession,
will—when they reach a certain strength—always adversely affect a wide rangeof financial institutions and markets, so that they have been included in the broadconcept of systemic risk.
The second key element in systemic events in the narrow sense is the mechanism through which shocks propagate from one financial institution or market tothe other. In our view, this is the very core of the systemic risk concept. Systematic shocks are equally important for the non-financial sectors in the economy.
The propagation of shocks within the financial system, which work throughphysical exposures or information effects (including potential losses of confidence), must be “special.” In what follows we shall look at the various propagation chains in banking and financial markets in much detail. However, from a
conceptual point of view it is important that the transmission of shocks is a natural part of the self-stabilising adjustments of the market system to a new equilibrium. What one has in mind with the concept of systemic risk (in the narrow
sense) are propagations that are not incorporated in market prices ex ante or canlead to general destabilisation. Such propagations, including those taking the formof externalities, may show particularly “violent” features, such as cumulative
reinforcement (“non-linearities”), for example through abrupt changes in expectations.
Obviously, both the occurrences of shocks as well as subsequent propagations
are uncertain. So the importance of systemic risk has two dimensions, the severityof systemic events as well as the likelihood of their occurrence. Strong systemic
events, in particular systemic crises, are low probability events, which might leadsome to consider them as less of a concern. However, once a crisis strikes theconsequences could be very severe.
This leads to another dimension of the concept of systemic risk, namely the
impact of systemic events occurring in the financial sector on the real sector,
more precisely on output and general welfare. One may distinguish horizontal
systemic risk, i.e. the concept which is limited to the financial sector alone(through the bankruptcy of financial intermediaries or the crash of financial
markets), from vertical systemic risk, where the impact of a systemic event on
output is taken to gauge the severity of such an event. In order to keep the scopeof the paper manageable we have to concentrate on horizontal systemic risk in thefirst place.99
See Lindgren et al. (1996) for a synthesis of the output effects of a large number of financial
crisis situations. As is evident from systematic shocks as one potential source of systemic crises(Table 1), the relationship between the performance of the real and financial sectors can go in both
directions (see section 3.1.1).

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2.2

Oliver De Bandt and Philipp Hartmann

The financial fragility hypothesis

Why is it then that systemic risk, in particular potential contagion effects, is of
special concern in the financial system? There are three interrelated features offinancial systems which can provide a basis for this “financial fragility hypothesis”: (i) the structure of banks, (ii) the interconnection of financial institutions
through direct exposures and settlement systems, and (iii) the information intensity of financial contracts and related credibility problems.
(i) Traditionally, commercial banks take fixed-value deposits that can bewithdrawn (unconditionally) at very short notice and lend long-term to industrial
companies (Gurley and Shaw, 1960). Normally, i.e. when the law of large numbers applies, only a small fraction of assets needs to be held in liquid reserves tomeet deposit withdrawals. This fractional reserve holding can lead to illiquidity
and even default, when exceptionally high withdrawals occur and long term loans
cannot be liquidated, although the bank might be fundamentally solvent in thelong run. Moreover, single bank loans do not have an “objective” market price.
Since usually the lending bank alone has most information about the real investments funded, they are largely non-fungible. (However, nowadays this statement
needs to be qualified to the extent that single loans to certain types of borrowers(or the credit risk incorporated) can be bundled and traded via securitisation
techniques (or credit derivatives). See, for example, Goodhart et al., 1998, chapter
5.) So, the health of a bank not only depends on its success in picking profitable
investment projects for lending but also on the confidence of depositors in thevalue of the loan book and, most importantly, in their confidence that other depositors will not run the bank. Notice that this “special” character of banks does
not apply to most other financial intermediaries, such as insurance companies,
securities houses and the like (see, for example, Goodhart et al., 1998, chapter
1).10 However, if banks and other intermediaries form groups, as is now more
often the case, the latters’ problems might still become a source of bank fragility.
Obviously, the more depositors are protected through some deposit insurance
scheme—as it exists now in most industrialised countries—, the less likely(ceteris paribus) confidence crises will become.11(ii) There is a complex network of exposures among banks (and potentiallysome other financial intermediaries) through the interbank money market, thelarge-value (wholesale) payment and security settlement systems. In fact, banks
tend to play a key role in wholesale and retail payment and settlement systems. At
certain points during the business day, these exposures can be very large, so thatthe failure of one bank to meet payment obligations can have an immediate
impact on the ability of other banks to meet their own payment obligations. Even
worse, a crisis situation can trigger difficulties in the technical completion of the10
The speciality of banks and their vulnerability to runs is widely recognised in the economic
literature, which will be surveyed in detail in section 3.
11
The problems associated with deposit insurance and their relationship to systemic risk areaddressed in section 2.4.

What is systemic risk today?

45

different steps of the payment and settlement process, which would amplify
effective exposures and “domino” effects. Various techniques used in securities
and derivatives markets, such as margin requirements and portfolio insurance, canalso account for large and immediate payments needs by banks and other intermediaries in times of large asset price changes. To the extent that financial conglomerates encompass banks and other financial intermediaries, securities orinsurance subsidiaries might also play a role in these interlinkages.12(iii) The third feature is the information intensity of financial contracts(Stiglitz, 1993). More precisely, financial decisions aim at the intertemporal
allocation of purchasing power for consumption purposes and are, therefore,
based on expectations on what the value of the respective asset is going to be in
the future or whether the future cash flows promised in a financial contract aregoing to be met. Hence, when uncertainty increases or the credibility of a financial commitment starts to be questioned, market expectations may shift substantially and “rationally” in short periods of time and so may investment and disinvestment decisions. For example, this can lead to large asset price fluctuations,whose sizes and sometimes also directions are virtually impossible to explain
through “fundamental” analysis alone. 13
These three features taken together seem to be the principal sources for theoccasionally higher vulnerability of financial systems to systemic risk than othersectors of the economy.

2.3“Efficient” versus self-fulfilling systemic events

Regarding the assessment of various systemic events, the information intensity offinancial contracts underlines the importance of the distribution of information
among the agents acting in the financial sector. General uncertainty and agents’awareness of potential asymmetries of information highlight the role that expectations can play for the occurrence or not of systemic events. In fact, systemic
events driven by expectations might be individually rational but not socially
optimal.
It is useful to distinguish three potential causes of narrow systemic events
related to asymmetric information and expectations. These are, first, the fullrevelation of new information about the health of financial institutions to the
public; second, the release of a “noisy signal” about the health of financial institutions to the public; and, finally, the occurrence of a signal which co-ordinates
the expectations of the public without being actually related to the health offinancial institutions (“sunspot”). Analogous cases apply to the release of information about asset values in financial markets, but for the purpose of illustration
12
Financial intermediaries’ interconnection through payment and settlement systems is further
studied in section 3.3.
13
Fundamental analysis attempts to explain or predict asset price changes through the factors
influencing the “intrinsic” values of assets. For example, “fundamentals” influencing shares arecompanies’ earnings, “fundamentals” influencing exchange rates are inflation rates.

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Oliver De Bandt and Philipp Hartmann

we shall continue with the example of banks.
Suppose that, hidden from depositors, a bank has made a number of loans thatturn bad, so that it is basically insolvent but continues to survive for some timesince it can roll over debts in the interbank market. Suppose further that otherbanks—having neglected to monitor their counterparties properly—develop
substantial exposures to it. If the information about these facts were then releasedin full, it would be rational for depositors to withdraw their funds and force thosebanks into liquidation. Ceteris paribus such an outcome, which can be denoted asa “fully revealing” equilibrium, would also be “efficient.”14
Second, suppose that the information about bad loans and interbank exposures
is not revealed in full but that depositors only receive imperfect information (a“noisy” signal) from some outside source, which from their point of view increases the likelihood for those facts. In such a situation it might still be rational
for them to try and withdraw their funds early and thereby force the default of
those banks. Whether the signal has been “right” or “wrong” would determine,ceteris paribus, whether this outcome is “efficient” or not. As it is triggered byimperfect information on fundamentals, this type of contagion could be denoted
as “information-based.”
Finally, suppose that the level of deposit withdrawals in itself provides animperfect signal for all depositors about the healthiness of banks and their counterparties. This fact enters an element of circularity in depositor behaviour that
results in the possibility for multiple equilibria. In these circumstances, even if all
the banks have been healthy ex ante, any event that co-ordinates depositors’
expectations about other depositors’ withdrawals might induce them to rush towithdraw and force those banks into liquidation. The related systemic event might
still have been “individually rational” ex ante, while the outcome in the form of aself-fulfilling panic or “pure” contagion is inefficient.
The asymmetric information problems also illustrate how financial problems
can build up over an extended period of time before an “efficient” or “inefficient”
crisis occurs. In other words, the systemic event is only the effect of a more
fundamental underlying problem, which has been hidden from policy makers or
the general public for some time. For example, reckless lending and bad loans
might have built up for some time in the banking sector before some explicit
shock triggers a systemic event. Similarly, stock market prices might have stayed
overvalued for an extended period until specific news bursts the bubble. Hence,
before we now turn to potential policy responses to inefficient systemic events, itneeds to be stressed that ex ante policies, measures trying to prevent a fundamental problem from actually arising (such as financial regulation and supervision or measures allowing market forces to be more effective), should always be
14
The efficiency holds under the assumption that there would not be any subsequent problems in
the payment system amplifying the problem beyond the group of unsound banks. In a somewhat
related vein, Kaufman (1988) points to a “benefit” of bank crises, forcing governments to step inand close all insolvent banks so that asymmetric information between the public and bank managers
is removed.

What is systemic risk today?

47

the primary defence line, so that it needs to be resorted to ex post policies in theform of crisis management in as few instances as possible.

2.4

Systemic risk and public policy

On the basis of the conceptual considerations presented so far, a first assessmentof the extent to which systemic risk is relevant for economic and financial policies can be undertaken. Musgrave and Musgrave (1973) have introduced the “classical” distinction of three functions for public policies: the allocation function, thestabilisation function and the distribution function. It appears that systemic risk is,
first, relevant for allocation policies. Strong systemic events, such as contagious
failures, may involve external effects; i.e. the private costs of the initial failure
can be lower than the social costs. As a consequence, individually rational bankmanagement may lead to a higher level of systemic risk than would be socially
optimal. This is one, maybe even the fundamental rationale, for the regulation andsupervision of banks. Notice that in this sense, the socially optimal probability ofbank failures is not zero. However, the socially optimal probability of “pure”
contagion (a self-fulfilling systemic event as described above) and certain casesof “information-based” contagion are. Apart from investor protection considerations, this is another fundamental rationale for the introduction of deposit insurance schemes. Moreover, to the degree that any systemic event might involve
payment and settlement system problems, which may amplify the strength andextent of externalities, it also provides a rationale for policies to ensure the safetyof those systems.15
Second, a systemic crisis affecting a large number of financial institutions ormarkets can—via a “credit crunch” or “debt deflation”—lead to a recession oreven to a depression. In such situations macroeconomic stabilisation policies,
such as monetary or fiscal expansions, may be used to dampen the recessionary
impact on the real economy. Interestingly, in the case of systemic risk, allocationand stabilisation problems can be closely intertwined. If contagion is very strong,then the microeconomic risk allocation problem can degenerate to a macroeconomic destabilisation.16
It is now widely recognised that public safety nets, whether they take the formof deposit insurance or lender of last resort facilities, bear the risk of creating
moral hazard. For example, if deposit insurance premia do not reflect the banks’relative portfolio risks, then the protection may incite the insured to take onhigher risks (Merton, 1976). Such effects may be countered by very effective
prudential supervision. However, to the extent that this is not successful, theinsured institutions will become more vulnerable to adverse shocks, so that the15

Private market initiatives may sometimes also offer a route to reduce systemic risk.
In principle, systemic crisis can also have distribution effects. Since the poor will haveinvested most of their small savings in bank deposits, etc. and not in physical property, for example,
and since they might be even less able to judge the health of a bank, they are particularly exposed tolose out. In virtually all industrialised countries at present this problem is dealt with in the form ofdeposit insurance schemes.
16

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Oliver De Bandt and Philipp Hartmann

likelihood of propagation across institutions may rise as well. This latter scenario
implies a higher level of systemic risk through inadequate safety net provisions.

3

Various facets of systemic risks

We now consider in greater detail the forms that systemic risk may take, distinguishing between banking, financial markets and payment systems. The focus ison “horizontal” systemic risk. The theoretical literature on systemic risk is surveyed in the light of these facets. Nevertheless, as indicated above, all thesedifferent elements are clearly related and interact with each other. In addition,
their relative importance may change over time. While systemic risk has traditionally been associated with banking markets, the growth of securities markets
has probably increased their role in the transmission of shocks.

3.1

Systemic risk in banking markets

As has been observed numerous times in the past, banks may, in the absence of asafety net, be prone to runs. On some occasions, individual runs may spill over toother parts of the banking sector, potentially leading to a full-scale panic. While
the theory of individual runs is well developed, the same does not apply to bankcontagion, which brings in the systemic component. One can distinguish two main
channels through which contagion in banking markets can work: the “real” orexposure channel and the informational channel.17 The former relates to thepotential for “domino effects” through real exposures in the interbank markets
and/or in payment systems. The information channel relates to contagious withdrawals when depositors are imperfectly informed about the type of shocks
hitting banks (idiosyncratic or systematic) and about their physical exposures toeach other (asymmetric information). In principle, these two fundamental channels can work in conjunction as well as quite independently. More elaborate
theories of bank contagion, such as Flannery (1996) or Rochet and Tirole (1996a),
which explicitly model these channels working through the liability side, have
only just now begun to be developed. We start out in the next sub-section with theold lending boom literature before coming to this incipient contagion literature.
3.1.1

Lending booms as a source of systemic risk

The early analyses of “systemic risk” emphasise the role of uncertainty (where
agents even have no information about the probability distribution of asset returns) as opposed to risk and the inability of banks to take the appropriate decisions in some circumstances (Kindleberger, 1978). The concept of credit overexpansion by Minsky (1977) is based on (contagious) euphoria and gregarious
behaviour. Banerjee (1992), Bikhchandani et al. (1992) as well as Avery and17See, for example, Saunders (1987, pp. 205f.).

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49

Zemsky (1998) introduce more formal models where each agent only observes theactions of other agents and uses Bayesian updating to derive his or her own
subjective probabilities of future returns. When pricing errors occur ex ante, such
behaviour can also lead to price discontinuities (Guttentag and Herring, 1984).
Myopia and short memory of agents about past events may also increase systemic
risk, since they can lead to an underestimation of the likelihood of large shocks. A
possible weakness of this literature, however, is the absence of a clear explanationof what triggers the initial deviation from the optimal behaviour as well as theburst of the bubble. In contrast, the relevance of such an analysis is more obvious
when structural changes affect the institutional or regulatory environment (see inparticular Davis, 1995), or when the institutional or regulatory and supervisoryenvironment leads to moral hazard in risk taking. The latter issue has been raisedin the context of the US S&L crisis (Kane, 1989) or more recently regarding thelending boom that partly led to the East Asian crisis (Krugman, 1998). Applying
modern corporate finance models of firms’ capital structure to banks, Dewatripont and Tirôle (1993) argue that banks’ excessive reliance on debt financing(partly related to their provision of retail payment services to a large number ofsmall and relatively uninformed depositors) also leads to more risk-taking in
lending.
This traditional lending boom literature clearly relates to the potentially slowbuild-up of structural problems in the financial sector. These structural problems
increase the likelihood as well as the severity of systemic events. However, itremains to investigate the precise conditions under which any bubbles burst andlending breaks down from one bank to another. Finally, many theoretical modelsof herd behaviour are not specifically formulated within a banking framework.
3.1.2

Bank runs versus bank contagion

The banking literature in the last 15 years has developed sophisticated models of
single banks’ fragility (see also point (i) in section 2.2). However, regarding
systemic risk the speciality of “the bank contract” is only part of the story. The
other parts are interbank linkages through direct exposures (and payment systems),
which can only be studied in a model of a multiple bank system (point (ii) in
section 2.2). In other words, one should distinguish between a “run” which involves only a single bank and a “banking panic” where more than one bank isaffected (Calomiris and Gorton, 1991). We will start by reviewing the traditionalbank run literature before covering the more recent models of contagion in multiple bank systems encompassing models applying the logic of the single bank run
literature to multiple bank systems, theories explicitly modelling physical interbank exposures, and extensions of credit rationing models to the interbank context.
The first class of models, following Diamond and Dybvig (1983), was designed to address the issue of the instability of the fractional reserve banking
system. Banks transform short-term deposits into long-term investments, with a50

Oliver De Bandt and Philipp Hartmann

liquidity premium, while depositors face an externality due to a “sequential
service constraint” (when depositors withdraw their deposits, a first-come-firstserved rule applies) and there is no market for investment or bank shares. A
fraction of bank customers experience a liquidity shock and wish to withdraw
their deposits. The crucial element is that the fear of withdrawal by a too large
number of depositors may trigger a run on the bank in the form of a self-fulfilling
prophecy.18 In the second class of models depositors are unable to value bankassets correctly, in particular when economic conditions worsen. In the model of“information based” or “efficient” bank runs by Jacklin and Bhattacharya (1987),
some informed depositors receive an imperfect signal that the risky investment
made by the bank may yield a lower than expected payoff. They may therefore
decide to withdraw their deposits, forcing the bank to liquidate its assets prematurely. In this model a trade-off arises in that equity contracts are vulnerable toasymmetric information but not runs (since they are conditional on the performance of bank assets) whereas (unconditional) deposit contracts are vulnerable toruns but not so much to asymmetric information.19 As indicated by Chari andJaghanathan (1988), agents can only identify the real performance of a bank ex
post. In their model, which provides a synthesis between the first two approaches,some agents receive information about the performance of the bank’s assets.
Although the other agents can observe the length of the “queue at the bank’sdoor,” they are not informed about the actual proportion of agents experiencing aliquidity shock, so that they may decide to run the bank when the queue is too
long.
Smith (1991) extends Diamond and Dybvig’s model to correspondent banking
in the US during the National Banking Era. In his model, local correspondentbanks may run the money center banks following a local shock. De Bandt (1995)
extends Jacklin and Bhattacharya’s (1987) model to a multiple banking systemand considers that an aggregate and an idiosyncratic shock affect the return onbanks’ assets. If depositors in one bank are the first to be informed about thedifficulties experienced by their bank, depositors in other banks will then revise
their expectations about the aggregate shock, hence the return on deposits in theirown bank. This creates a channel for the propagation of bank failures. Temzelides(1997) develops a repeated version of the Diamond and Dybvig model where
agents adjust their choices over time through learning from past experience withthe banking system. One of the two Nash equilibria of panic/no panic is selected
and learning introduces some state-persistence. The author also introduces a
multiple banking system, where depositors observe bank failures in their own
region and may decide to shift to the panic equilibrium for the next period. In thisframework, more concentrated banking systems are less sensitive to idiosyncratic
18
In this model banks’ deposit contracts are seen as insurance against liquidity shocks. Both“run” as well as “no-run” are possible Nash equilibria.
19
In general share contracts are superior to deposit contracts in the model. However, when theunderlying asset is not too risky, a deposit contract, even with possible runs, may be welfare
superior to a share contract.

What is systemic risk today?

51

shocks and are therefore less prone to contagious panics. As for the literature on
lending booms, it is clear that the macroeconomic environment plays a crucialrole in the transmission of shocks with possible feedback effects between thebusiness cycle and the banking sector’s profitability.20 In particular, through theunconditional character of deposit contracts and the great sensitivity of present
asset values to interest rate risk large macroeconomic shocks may easily lead tosimultaneous problems in a large number of banks (systemic crisis in the “broad”
sense).
A further step are models of the interbank market and direct exposures, whichhave been developed recently against a background of a substantial growth inuncollateralised interbank lending, in particular at the international level. Rochet
and Tirole (1996a) present a model of physical exposures in the interbank market.
In their model, banks face funding shocks and lending banks have a natural
incentive to monitor the banks to which they are exposed. This creates a linkage
between the different banks. Formally, banks experience a solvency shock in theinterim phase of a three-period model. When banks are short of reserves, theyborrow funds in the second period (“date 1”) in order to carry out their project.
There is moral hazard on the part of the banks’ shareholder-managers as it is notpossible to contract on the level of effort provided by the banker. Interbank peer
monitoring can provide the right incentives. If monitoring is exerted during thesecond period (“date 1”) and reduces the bank’s private benefit from shirking, thefailure of one bank jeopardises the profitability of the lending bank and closure
decisions of the different banks are intertwined. Domino effects and propagationof failures across banks may occur, since liquidity shocks affecting one bankincrease the probability that other banks may be liquidated. “Chain” liquidations
affecting a fraction of the banking system are likely to occur, although this is not
explicitly mentioned. Only the global collapse of the whole banking system
receives an explicit treatment by the authors, along the following lines: undersome realisation of the liquidity shocks, the optimisation of banks’ and depositors’ utilities yields exactly two maxima (all banks fail/no banks fail). In thisframework, a small increase in a bank’s funding shock may imply the closure of
the entire banking system.
3.1.3

Credit rationing in the interbank market

As conjectured by Davis (1995), the literature on credit rationing can be extended
to the relationships among banks in the interbank market. If banks face a demandfor credit by banks of unknown quality ex ante (adverse selection), lenders may
decide to ration the amount of credit to all banks instead of raising interest rates,in order to avoid that the proportion of bad risks increases with interest rates. In
the same vein, Flannery (1996) suggests a model of adverse selection in theinterbank market. It is assumed that banks receive imperfect signals about the20

See in particular Bernanke and Gertler (1990) as well as Mishkin (1991).

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Oliver De Bandt and Philipp Hartmann

quality of prospective borrowers. In this simple model, banks only lend when theyreceive a “good” signal. However, on some occasions, following a large shock in
the financial system, banks may become uncertain about the accuracy of theirassessment of the borrowing banks’ credit quality. As they feel less able to distinguish between “good” and “bad” banks, lenders raise interest rates across theboard. If the loan rate becomes too high, “good” banks might not be able to repay
their interbank loans any more, so that illiquid but solvent banks may go bankrupt.
There is no successive process of propagation in this model, so we include it in
our concept of systemic risk in the “broad sense.”

3.2

Systemic risk and financial markets

The role of financial markets is perhaps the most difficult element in the analysis
of systemic risk. On the one hand, their tremendous growth over the previous
decades has made them much more important, even in the more bank-based
financial systems of Continental Europe. On the other hand, despite a generalawareness about the occasional occurrence of market crashes, their role in truly
systemic events has not really been explored in a systematic fashion. This contrasts with the existence of some theories of systemic risk in banking markets andsome practical studies of systemic risk in payment and settlement systems.
In fact, markets are different from financial corporations. They do not gobankrupt, as institutions can.21 So while there can be price crashes and propagation of them from one market to another, the main concern will be with the shocks
that financial market crashes and temporary liquidity crises—be they contagious
or not—impose on the rest of the financial sector and the real economy. Due tothe high fungibility of the instruments traded in secondary markets their prices
can be very information sensitive and fluctuate sharply. Whereas financial institutions and agents acting in the real economy should be able to adapt to andprotect themselves against the normal amplitude of financial market price changes(“volatility”), this cannot be taken for granted for some truly extreme and generalfluctuations. These extreme events may be, among others, the consequence of the
burst of a “bubble,” possibly reinforced by certain trading strategies, such as
program trading and positive feedback strategies.22
In the remainder of this sub-section the potential for contagious financial
market crashes is reviewed first (systemic risk in financial markets in the narrow
sense), and then financial market crashes and liquidity crises as shocks to financial institutions and the real economy are considered.

21
While the shares or bonds of a defaulting company will disappear from markets, it is hard to
imagine a situation in industrial countries in which a previously existing stock, bond or foreignexchange market disappears, let alone the disappearance of several of those markets through contagion.
An exception might be some segments of high-risk markets, which might disappear after a crisis.
22
See De Long et al. (1990) as well as Gennotte and Leland (1990) for models showing how
these strategies can cause multiple equilibria and non-linearities in financial market prices.

What is systemic risk today?

3.2.1

53

Contagion across financial markets

Our first step is the discussion of contagion effects between financial markets
leading to a systemic event in the narrow sense. This may be due to technicalfactors (e.g. collateral sell-offs may lead to the propagation of price changes
across markets or arbitrage between cash and future markets may cause comovements between the two markets.23 However, we concentrate here on contagion based on the revision of expectations. In spite of the existence of a unified
framework, a fraction of the post-1987 finance literature has attempted to uncoverpossible contagion effects among international securities markets, defined either
as changes in securities prices (conditional mean or variance) that affect othercountries beyond what is justified by fundamentals, or unexpected volatility spillover effects during crisis periods. As for banking markets, we review successively
what we identified in section 2.1 as two main channels of propagation, namely“information based” and “pure” contagion.
3.2.1.1

Contagion based on noisy signals under asymmetric information“Information-based” contagion should be distinguished from “fully revealing”
equilibria, that we define as connections between securities markets throughfundamentals. In particular, in integrated financial markets, there is full risk
sharing and (national) systematic disturbances or shocks to fundamentals aretransmitted to other markets. In the seminal model of King and Wadhwani (1990),
information is “not fully revealing” and agents in different markets have access todifferent sets of information. In particular, investors make decisions on the basisof information from prices in other markets as it is less costly to process information accruing in the form of unanticipated changes in asset prices than “news” on
Reuter’s screens. There is therefore a significant effect on prices in market i of an
idiosyncratic shock in market j. Hence, mistakes in one market are transmitted toother markets. They argue that if a shock creates more volatility but is not generated by “news” (e.g., as during the 1987 stock market crash), agents are led to pay
greater attention to other markets in an attempt to determine the effect of theshock on the demand for equity. Shiller (1995) also suggests a similar model
where traders around the world have access to the same information, but process
it differently, based on their own national experience. Individual (national) reactions to a systematic shock provide signals about the global implications of theinitial shock. Dramatic conclusions drawn by the operators in one country lead
operators in other countries to revise their expectations, hence creating an information cascade.
There is, however, a debate in the literature about the identification of therelevant changes in “fundamentals,” as opposed to “noisy signals,” since a broad
23
Referring to the introduction of futures markets Guesnerie and Rochet (1993) make thedistinction between gains in terms of volatility reduction and the greater difficulty for agents to coordinate expectations.

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Oliver De Bandt and Philipp Hartmann

concept of “fundamentals” would tend to downplay the role of asymmetric information and the process of progressive revelation of information to the market andto equity prices. Whereas fundamentals are often defined as the main macroeconomic indicators that may have an effect on returns in securities markets,
fundamentals are extensively defined by Hamao et al. (1990) as the whole information set of traders. Contagion can occur across markets given the noncoincidence of trading periods (e.g. the Tokyo market closes before the New York
market opens). If one decomposes daily returns into Close-to-Open and Open-toClose and if it is assumed that currency markets are efficient, any information
occurring before the opening of a trading session should be fully included in the
opening price and should not affect the Open-to-Close return. This provides a testof contagion (see section 4.2).24
3.2.1.2“Pure” contagion across financial markets

Finally, “pure” contagion across markets may also be present. Currency markets
with managed floating are the most likely to face such contagion effects as regulation may create some market incompleteness, giving rise to speculative attacks
on currencies. However, the analysis is usually limited to a single currency. In
particular, following models based on fundamentals (Krugman (1989), Gerlach
and Smets (1995)25), Bensaid and Jeanne (1997) show that a sunspot is sufficient
to destabilise a fixed exchange rate as long as the cost of leaving the arrangement
is finite. More recently, Masson (1998) suggests a model of contagion acrosscurrency markets, which corresponds neither to common causes (labelled “monsoonal effects”), nor to spillover effects driven by fundamentals. In order toexplain the effect of the currency crisis in Mexico and Thailand, the author uses a
two-country model of balance of payments, which exhibits multiple equilibria forthe probability of devaluation. Multiple equilibria only occur when fundamentals
are poor. This formalises the intuition that sunspots lead speculators to re-evaluate
their assessment of the fundamentals. Following the failure of a single fixedexchange rates arrangement, traders realise that the other arrangements are also
fallible, so that speculation is transmitted to other weak currencies.
24
One related question is the process of change in fundamentals or the arrival of “news.”
However, such a question has not been addressed in a systematic way in the finance literature. One
can only report the classification suggested by Lin and Ito (1995) who argue that one should
distinguish between two causes of increasing correlation among international stock returns: (i) an
increase in price volatility which signals a faster rate of transmission of news to the market andwhich is consistent with securities market efficiency and (ii) higher trading volumes which indicate
more heterogeneity among traders and induce contagion of liquidity traders’ sentiments. However,such an identification scheme is only assumed by the authors and not derived from an explicit model
encompassing the two sources of shocks. In particular, it could be argued that increasing volatility
might also, to some extent, measure information heterogeneity and create informational contagion.
25
Gerlach and Smets (1995) offer a model of contagion between two countries connected
through trade in goods and financial assets. A successful speculative attack against one currency
boosts the competiveness of that country at the expense of its neighbours which are likely to be its
direct competitors. This is likely to weaken the currency of the neighbouring countries that may
become subject to a speculative attack.

What is systemic risk today?

55

To conclude, it appears that securities markets may constitute a crucial vector
for the transmission of large systematic shocks. However, if the finance literature
has achieved substantial progress in the understanding of large swings, nonlinearities, multiple equilibria occurring in individual securities markets, muchremains to be done regarding the transmission of shocks across markets and to
institutions. In particular serious identification problems need to be overcome todistinguish between the efficient response to news and over-reaction of securities
markets.
3.2.2

Financial markets as sources of systematic shocks

Large general price fluctuations or liquidity crises are themselves shocks tofinancial institutions and other agents. Extreme events in any of the major financial markets (stock market, government bond market, etc.) affect a large numberof agents at the same time and are therefore of a “systematic” nature. Such systematic shocks from the markets will be even more widespread if they are contagious across markets, as discussed in section 3.2.1.
3.2.2.1

Shocks to financial institutions

In the recent past formerly “commercial” banks have become more and more
involved in financial market trading activities (as opposed to traditional lending).
Their larger trading books potentially lead to larger exposures to shocks originating in those markets. This implies that the structurally higher systemic risk inbanking markets due to fixed value deposits and cross-exposures, as described in
sections 2.2 and 3.1, will be more dependent on financial market fluctuations thanhas been previously the case. Similarly, it may have also become more dependent
on the safety of the security settlement process (see section 3.2.2). The same
applies to the banks’ participation in financial conglomerates where other units
are involved in securities activities.
Investment banks, securities houses, hedge funds, etc. are generally morerisky than traditional commercial banks (e.g. in terms of earnings volatility), but
as separate entities they are less vulnerable to the type of contagion that may
affect the latter.26 However, to the extent that they are involved in interbank
money market borrowing their failure due to a large shock originating frommarket crashes may still spill over to the banking system (see section 3.1.2).
Alternatively, various events in financial markets (such as the failure of alarge institution or a significant price fall) may increase uncertainty about theability and willingness to trade by the main participants acting in these markets,in particular among market makers (Davis, 1994). Somewhat analogous to the26
One study investigates the effect of the announcement of OTC derivative losses by four clientsof Bankers Trusts on other investment banks’ stock prices during the first 9 months of 1994 (Clark
and Perfect, 1996). The results tend to indicate that capital markets discriminate between derivative
dealers on the basis of their exposure levels.

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Oliver De Bandt and Philipp Hartmanncase of the interbank money market discussed above, liquidity in the respective
financial instruments traded may dry up through adverse selection (Flannery,
1996). For example, market makers might increase bid-ask spreads to reduce thelikelihood of being hit by a transaction (price rationing) or even “refuse” to tradeat all (quantity rationing). Such a liquidity “freeze” could involve a systematic
shock on all those banks and non-bank financial institutions, whose risk management strategies depend on the ability to trade in these markets.27
3.2.2.2

Shocks to the real economy

Already Fisher (1933) in his debt-deflation theory examined the connection
between the poor performance of financial markets and the Great Depression.
One link between financial markets and the business cycle was also formallyexplained by Kiyotaki and Moore (1997) through the effect of depressed asset
prices on agents’ ability to borrow against available collateral. Their model does
not address the issue of systemic risk, but rather stresses explanations for businesscycle fluctuations. However, the same mechanism might work with greater
strength in times of financial market crashes.

3.3

Systemic risk in payment and settlement systems

By providing the technical infrastructure through which banking and securities
market transactions are settled, payment and settlement systems determine to an
important extent the physical exposures among financial institutions. In a way,
looking at payment and settlement systems is like looking at the network ofinterbank exposures with a magnifying glass. Hence, depending on their internalorganisation they also determine how shocks may propagate through the financial
system, in particular how severe contagion can be. The analytical literature on
systemic risk has largely overlooked their importance until very recently. The
fundamental underlying risks in these systems are similar to those encountered byfinancial institutions in general: operational risk (such as the failure of a computer,as for the Bank of New York in 1985), liquidity risk (reception of final or “good”
funds, not being realised at the desired time but at an unspecified time in the
future), and credit risk (failure of an insolvent participant with a subsequent lossof principal).
3.3.1

Interbank payment systems

There are three main types of interbank payment systems: net settlement systems,
gross settlement systems and correspondent banking. In what follows we shallfirst describe “prototypes” of these systems and then refer to the most importantpractical deviations from these types. In net settlement systems payments among
27
A recent event that has raised these issues in practice is the bail-out of Long Term CapitalManagement, a large hedge fund, in September 1998.

What is systemic risk today?

57

members are collected over a certain period of time, e.g. a whole day or several
hours, and at the settlement time the gross payments between members are netted
against each other, so that only the net balances have to be settled with finality.
With bilateral net settlement the members effectively remain the only counterparties to each other, while in multilateral net settlement systems debit and credit
positions are accumulated vis-à-vis a central counterparty (usually a clearing
house) until they are offset at the settlement time. Net settlement systems involve
relatively low costs, because actual settlement is relatively rare—normally occurring only once at the end of the day (and in some cases twice a day)—and thus
liquidity costs are low. Because of the more limited number of direct counterparties, these cost savings are usually more pronounced in multilateral systems thanin bilateral netting. The netting of reciprocal gross positions between institutions
can considerably reduce the effective debit positions, and thereby systemic risk,
as compared to pure gross settlement undertaken on the same time scale, where
incoming and outgoing payments are settled independently (without any netting).
However, without additional provisions, net settlement systems are still comparatively vulnerable to systemic risk, since gross exposures accumulating between
settlement times can become very large.
In real-time gross settlement systems (RTGS) payment finality is virtually
immediate for every transaction, so that the systemic risk from unsettled claims
appears to be very limited, at least at first glance. Due to the heavy charge for
intra-day liquidity management (in order to have always enough liquid funds
available during the day) it is comparatively costly for member banks. Moreover,banks’ ability to pay out may depend on the timeliness of incoming payments, butcounterparties may sometimes have the incentive to delay outgoing payments.
Therefore, RTGS can be characterised by relatively frequent queuing phenomena,
which can lead to wide-spread liquidity (“network”) externalities or even system“gridlock” when participants economise on their intra-day liquidity or default.
This shows that even RTGS may not be totally free of systemic risk.
Most real-life systems have specific additional institutional features in orderto reduce systemic risk or liquidity costs (and gridlock risk) in net and grosssystems, so that both types become actually more similar. For example, net settlement systems now often introduce caps on the exposures between settlement
times and loss-sharing arrangements between members for cases of defaults.
Regarding the latter, “decentralised” multilateral net systems are to be distinguished from “centralised” systems, where the central counterparty takes over therisks and can, therefore, default itself. Also, legally binding netting-arrangements
can apply for the periods between settlement times or the number of settlement
times during the day could be increased.28 In order to reduce the liquidity costs ofreal-time gross systems the possibility of intra-day overdrafts vis-à-vis the settle-

28
The legal enforcement of these netting arrangements can be particularly difficult forinternational transactions. For example, in some jurisdictions a liquidator may be able to engage in“cherry picking” favouring the general creditors of a failed institution (BIS, 1990).

58

Oliver De Bandt and Philipp Hartmannment agent are now often allowed. Since they are a potential source of systemic
risk, these overdrafts are either secured through collateral requirements, as will be
the case for the Trans-European Automated Real-time Gross settlement Express
Transfer System (TARGET) and the connected national RTGS, or through daylight overdraft fees, as in the case of Fedwire in the United States. Alternatively,
routine queuing facilities can be established, which however imply similar risks
as net settlement systems.
Correspondent banking relationships appear to be very diverse. Correspondent banks provide payment services for groups of usually smaller or foreignbanks, which do not have cost-effective access to the primary domestic net or
gross systems. Each of the latter groups of banks settles bilaterally with thecorrespondent via debits and credits on nostro and loro accounts, whereby gross
exposures can be netted against each other.29 Therefore, the failure of an important correspondent bank can directly affect a large number of those institutions.
Moreover, correspondent banking is used by large credit institutions for international transactions. In this respect, it could become one of the major channels forthe transmission of the so-called Herstatt risk (see the next section).30
There is only an incipient literature of theoretical models describing the risksof different payment system arrangements. Angelini (1998) models profitmaximising banks’ behaviour in an RTGS where intraday liquidity is available
from the central bank against a fee proportional to the size of the overdraft.
(Following the example of the US Fedwire system, overdrafts are not collateralised.) Delaying payments has also a cost in terms of customer dissatisfaction.
Angelini derives in the framework chosen that the competitive (Nash) equilibrium
is not welfare optimal, since the cost of intra-day credit induces banks to delay
payments rather than to draw on the overdraft facility. These payment delays
result in network externalities, since payees attempt to free ride on other banks’
reserves, thereby reducing overall liquidity. (However, the author does not address explicitly the question whether a “gridlock” equilibrium can exist, in which
payment activity comes to a standstill; a stronger form of systemic risk). He
concludes that in RTGS intra-day overdrafts (by the central bank) must be madesufficiently cheap, so as to remain lower than banks’ customer dissatisfaction
costs through payment delays. Moreover, he suggests that banks could be induced
to pay earlier during the day via variable overdraft fees, which penalise latepayments. In contrast, Humphrey (1989) has argued that payment delays in grosssystems with uncollateralised overdraft facilities may be desirable to reduce theactual overdrafts and therefore systemic risk or the costs of the system guarantor.
Schoenmaker (1995) compares multilateral net settlement systems (à la US
CHIPS) and collateralised RTGS systems both theoretically and through the29
In a way correspondent banking can be seen as a step from bilateral net settlement towards
multilateral net settlement, although happening on a smaller scale.
30
For other reviews of payment system arrangements and the risks involved, see FolkertsLandau (1991), Borio and Van den Bergh (1993), Summers (1994), Berger et al. (1996), Rochet andTirole (1996), Schoenmaker (1996), Kobayakawa (1997) and Rossi (1997).

What is systemic risk today?

59

simulation of average costs with real transactions and historical bank default data.
It turns out that the average costs through settlement failures (defined as historicalfailure rates times maximum open intraday positions) are higher in the net than in
the gross system, but those through settlement delays (or gridlock) and collateralrequirements are lower in the net systems. This might explain why central banks
often prefer “safer” gross systems while market participants favour “less costly”
net systems, and it also reflects the trade-off between risks and costs described inBerger et al. (1996). In particular, Schoenmaker explicitly derives the potential
occurrence of systemic events in the form of gridlock in the RTGS variant(proposition 4.1).
Elaborating on Schoenmaker’s comparative approach and using a theoreticalframework akin to Angelini’s, Kobayakawa (1997) provides a broad analysis ofmultilateral net settlement and both types of RTGS, with full collateralisation of
intraday overdrafts (“EU type”) and with fees on uncollateralised overdrafts (“UStype”). However, like Angelini he focuses on their relative efficiency and (apartfrom externalities through payment delays) he does not derive explicitly any
systemic events that might occur.
In contrast, in a careful theoretical study of foreign exchange netting (see also
section 3.3.2) Yamazaki (1996) focuses entirely on the relative importance ofsystemic exposures in bilateral net settlement as compared to multilateral net
settlement (decentralised variant with loss-sharing among participants andwithout a clearing house). He establishes that for single failures multilateral
netting reduces other banks’ exposures as compared to bilateral netting, if theinitial loss is not “extreme.” However, when a chain reaction of failures occurs,
he shows that there are plausible cases in which the systemic event under multilateral netting is more severe than under bilateral netting. Moreover, he points to
moral hazards that can be associated with multilateral netting.
In a more abstract model, Freixas and Parigi (1998) (building on McAndrews
and Roberds, 1995) introduce geographical consumption preferences in a Diamond-Dybvig-type model, which lead to “interbank payments” between two
regions. With “gross settlement” banks have to liquidate investments to the fullamount of outgoing payments in the same period, which imposes a relatively highopportunity cost through foregone interest on investments. With “net settlement”
the banks can, first, offset incoming and outgoing payments and, second, extend
credit lines to each other in order to finance future consumption of “foreign”
consumers. In this framework the “gross system” is free of contagion but exhibitshigh opportunity costs. The “net system” exhibits systemic risk and potential
welfare losses in so far as inefficient banks may stay open for longer.
3.3.2

Foreign exchange and securities settlement systems

In contrast to national interbank payments, foreign exchange and securities transactions involve the settlement of two “legs.” Foreign exchange transactions
involve the opposite payment of the same principal amount in each of the two

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Oliver De Bandt and Philipp Hartmanncurrencies, and securities transactions involve the “delivery” of the security in
one direction and the opposite “payment” of funds in the other, which can enhance credit and liquidity risks. The credit risk resulting from defaulting counterparties in these transactions may not only cause the loss of principal (“principalrisk”), but it has also a market risk component known as “forward replacement
cost,” the potential loss implied by having to replicate a transaction in the market
when the counterparty has defaulted and the market price has become less advantageous for the non-defaulting party.31
Asynchronous settlement of the two legs leads to additional channels throughwhich contagion between financial institutions and markets can work. Regarding
international transactions the existence of different time zones can create “Herstatt risk,” the danger that one leg is already settled while the counterparty incharge of settling the other leg defaults before the systems in the respective othertime zone already operate. Similarly, in the case of national securities market
transactions, the payment leg through interbank transfer systems may have a
different timing than the delivery leg of Central Securities Depositories (CSDs).
Increased concerns about principal risk in securities settlement has led to major
initiatives to achieve “delivery versus payment” (DVP), the simultaneous settlement of both transaction legs (Committee on Payment and Settlement Systems(CPSS), 1992). On the other hand, it is also true that DVP mechanisms by connecting real time payment systems and securities settlement systems accelerate
the transmission of risks from one system to another (i.e. if settlement of cash
cannot take place because of a problem in the settlement system securities will
not be settled either and vice versa). Alternatively, securities can also be used tooffset other securities transactions in a simultaneous fashion (“delivery versus
delivery,” DVD).
The CPSS identified three main approaches to securities settlement systems in
G-10 countries: 1) systems that settle both securities and funds on a gross basis
and in a simultaneous fashion, 2) systems that settle securities on a gross basis
and funds on a net basis at the end of the settlement cycle, and 3) systems that
settle both legs on a net basis in parallel at the end of the settlement cycle. Practical implementations of the first approach share many of the risks of RTGS ininterbank payments and operational responses to those risks are very similar (e.g.
collateralised intraday or even overnight credit facilities). In most implementations of the second model the risk of unsettled payment legs is limited through“assured payments” via guarantors, which however could fail themselves. In
many type 3) systems the failure of a counterparty to settle a net funds debit
position leads to an unwinding procedure, which may create considerable systemic risk through liquidity pressures on other participants. Therefore, in several
cases the systems operator or a clearing corporation guarantees the completion of
settlement.
31
The systemic dimension of principal risks associated with bilateral and multilateral forex
netting systems are studied in the paper by Yamazaki (1996) discussed in section 3.3.1.

What is systemic risk today?

61

CSDs, which play the role of the settlement agent in national securities transactions, may sometimes also be at risk of failing, potentially implying substantial
systemic repercussion due to “custody risk.” If claims of financial institutions on
the securities in custody with the depository are not clearly segregated, some ofthem may experience unexpected losses. A similar problem may arise with
“global custodians” on the international level. These custodians, usually big
investment banks, maintain accounts with the different national CSDs in order to
execute securities transactions for other banks which do not have access to foreign CSDs. While playing an important intermediary role in connecting separated
national CSDs, their failure can be an element in the international transmission ofcrises since, unlike CSDs, global custodians are normally also large participantsin payment systems.
The payment and the delivery side of securities transactions show the potential for contagion working from members of interbank payment systems to thoseof securities settlement systems and vice versa. In fact, most credit institutions areactive in both interbank payment and securities settlement systems. Experiencesfrom the 1987 stock market crash reported in Brimmer (1989) and Bernanke(1990) show that these types of cross-system propagations can easily become real
in a major crisis. However, we are not aware of any theoretical models describing
the particular risks of securities settlement systems in a rigorous way.
The risk of cross-system spillover effects may be more severe between foreignexchange settlement and national interbank payment systems. The CPSS (1996,
fn. 3) reports system operator estimates saying that “FX settlements account for
50% of daily turnover value in CHIPS and CHAPS, 80% of the daily turnovervalue of EAF, and 90% of the daily turnover value of SIC.” Industry groups suchas FXNET, S.W.I.F.T. or VALUNET provide various bilateral foreign exchange
netting services for various groups of banks. ECHO and Multinet provide multilateral netting services. A major new development will be the establishment of acontinuously linked settlement (CLS) bank by 20 major banks in the forex settlement business.

4

Empirical evidence on systemic risk

In this section we survey the existing empirical evidence on systemic events andsystemic crises in the light of the concepts developed in Section 3, mainly focusing on rigorous empirical analyses of contagion. The objective is to identify how
much we know about the pervasiveness of the different elements of systemic risk
in different countries as well as on the international platform. Another objective isto detect those areas of the empirical analysis of systemic risk, which have not yet
received enough attention to be properly understood. This will point us to necessities for future research efforts.

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4.1

Oliver De Bandt and Philipp Hartmann

Evidence on bank contagion

As has been pointed out in Section 3, the risk of contagious bank failures may beviewed as the “classical” case of systemic risk. Testing for bank contagion
amounts to testing whether “bad news” or the failure of a specific bank (or groupof banks) adversely affects the health of other banks. The literature that hasdeveloped around this can be separated into several groups. One group of papers
tries to link bank failures with subsequent other bank failures directly. A second
group studies the relationship between failures or “news” and other banks’ stock
market values. A third group looks at the link between “news” or failures anddeposit withdrawals at other banks. A fourth group analyses the effect of “news”
or failures on the probability of other banks’ defaults, as perceived by market
participants and reflected in risk premia in interbank lending. Finally, one canmeasure the physical exposures among operating banks (or between those andbanks which have been “bailed out” by the government) to evaluate whether adefault would render other banks insolvent. We proceed in successive order.
4.1.1

Intertemporal correlation of bank failures

The common ground of this first branch of the bank contagion literature is a test
for autocorrelation in bank failures. Basically, the rate of bank failures in a period
t is regressed on the rate in the previous period (t-1) and a number of macroeconomic control variables. Provided that all macroeconomic shocks are effectively covered by the control variables a positive and significant autocorrelation
coefficient indicates that bank failures and periods of tranquility cluster over time,
which is consistent with the contagion hypothesis. Since the safety net provisions
in modern financial systems, such as deposit insurance schemes and lender-oflast-resort facilities tend to prevent that a single bank failure can lead to effective
failures of competitors, these tests have to be undertaken for historical periods incountries without strong (public) safety nets.
Grossman (1993) finds with a simple OLS regression analysis of quarterly US
data for the period between 1875 and 1914 (i.e. before the establishment of theFederal Reserve System) that a 1 per cent increase in failures in a quarter led on
average to a 0.26 per cent increase in the following quarter. Hasan and Dwyer(1994) and Schoenmaker (1996) have substantially refined this approach andprovide more evidence of intertemporal failure clustering in “free banking”
markets. Hasan and Dwyer (1994) apply a probit analysis to data from the US
Free Banking Era (1837 through 1863). Depending on the crisis considered in thisinterval and the respective region they find evidence compatible with contagion
or not. By applying an autoregressive Poisson (count data) model to the numberof bank failures, Schoenmaker (1996) finds strong results for a sample of monthly
data covering the second half of the US National Banking System and the earlyyears of the Fed (1880 through 1936). The autoregressive parameters are strongly
significant up to a lag of 3 months and they increase in size and significance forthe sub-sample encompassing the Great Depression, while macroeconomic fac-What is systemic risk today?

63

tors appear to become less informative for the prediction of failures.
In sum, this approach seems to have been relatively successful in making thecase in favour of the contagion hypothesis. However, the main disadvantages ofthis approach are that, first, the negligence of macroeconomic factors exhibiting
autocorrelation themselves would cloud any “evidence” of contagion and, second,it can only detect intertemporal contagion at the frequencies of macroeconomic
data and not at shorter time intervals.
4.1.2

Event studies on stock price reactions

The most popular approach to test for contagion effects turned out to be event
studies of bank stock price reactions in response to “bad news,” such as theannouncement of an unexpected increase in loan-loss reserves or the failure of acommercial bank or even of a country to serve its debt. The presence of contagionis usually tested by comparing the “normal” return of a bank stock, as predictedby a standard capital market equilibrium model (such as the CAPM) estimatedwith historical data, to the actually observed returns at the announcement data or
during a window around this date. “Bad news” for a bank i leading to significantly negative “abnormal” returns of another bank j is interpreted as evidence infavour of contagion.
The forerunners in applying this approach were Aharony and Swary (1983)
who studied the effects of the three largest bank failures in the United States
before 1980: United States National Bank of San Diego (1973), Franklin National
Bank of New York (1974) and the Hamilton National Bank of Chattanooga(1976). The sources of each of these three failures seem to have been of a rather
idiosyncratic nature, related to in-house fraud, illegal real-estate loans or foreignexchange losses. The Franklin National case, the failure of the 12th largest US
bank at the time, caused substantial negative abnormal returns in money-center,medium-size and small banks, whereas no external effects of the smaller twoother cases occurred.32
Swary (1986) applies the same approach to the Continental Illinois National
Bank failure in 1983-84, the 8th largest bank in the United States. Although larger
than Franklin National and confronted with somewhat less idiosyncratic problems(bad domestic and international loans), negative abnormal returns of 67 other US
banks turned out to be weaker and somewhat proportional to these other banks’
own pre-crisis solvency situations. Wall and Peterson (1990) find that part ofthese negative stock market reactions can also be explained by more general “badnews” arriving about the Latin American debt crisis. Jayanti and Whyte (1996)
show that stock market values of British and Canadian banks with significant
LDC debt exposures were also adversely affected by Continental’s failure but not
those British banks which were unexposed to debt crisis countries. Peavy and32
However, Aharony and Swary caution that there were a number of other banks which faced
foreign exchange losses similar to those of FNBNY shortly after the switch to floating exchange
rates (notably Germany’s Herstatt bank).

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Hempel (1988) show that the Penn Square Bank failure of Oklahoma in 1982 had
only regional repercussions.
In a similar vein, Madura and McDaniel (1989) analyse the effect of the 3billion-dollar loan-loss reserve announcement of Citicorp in 1987 on the stock
prices of the 11 other US money-center banks, which also issued loan-loss announcements later in the same year. Their results indicate that most of the losses
had been anticipated earlier by the market. Docking et al. (1997) study the effectof 188 loan-loss reserve announcements by nine leading money-center banks and390 announcements by 102 regional banks in the United States from 1985 to 1990.
It turns out that there is little impact of money-center bank announcements onother money-center banks’ stock prices, but regional banks’ announcements (fromcertain areas) can have detrimental effects on other regional or money-centerbanks. These results are compatible with the hypothesis that investors better
anticipate unfavourable announcements from the large and “visible” moneycenter banks than from regional banks.
The early results of adverse “external” stock market reactions to “bad news”
triggered a debate about whether they can be interpreted as evidence of “pure”
contagion effects or whether they rather reflect rational investor choices in response to the revelation of new information. In a series of papers the strength ofabnormal returns during the international debt crisis of the 1980s was linked tobanks’ own exposures to problem countries. Cornell and Shapiro (1986) undertook cross-sectional regressions for 43 US bank stocks and for various subperiods during 1982 and 1983 and Smirlock and Kaufold (1987) performed
seemingly unrelated regressions for 23 exposed and 37 non-exposed US banks
around the 1982 Mexican debt moratorium. Musumeci and Sinkey (1990) and
Karafiath et al. (1991) study the effects of the 1987 Brazilian debt moratorium on
US bank stocks. The former use an OLS cross-section regression for 25 banks,
the latter a Generalised Least Squares (GLS) cross-section regression for 46 bankholding companies. Madura et al. (1991) assess the impact of Citicorp’s announcement of substantial loan-loss reserves on the share prices of 13 large
British banks. The general result of this debate was that abnormal returns varied
in proportion to banks’ exposures to problem countries, which is consistent withthe hypothesis of rational investor choice.
Since most of these results are found for US data, an interesting question to
ask is whether they carry over to other financial systems. Unfortunately, not muchseems to have been published for other countries. An exception is Gay et al.
(1991) who chose to examine bank failures in Hong Kong during the 1980s.
These cases are interesting, because first Hong Kong did not have an explicit
deposit insurance scheme (which might dampen any contagion effects) and second at least two of the three failures studied (Hang Lung Bank in 1982 and Overseas Trust Bank in 1985) seem to have had rather idiosyncratic sources, such as
management misconduct and embezzlement, while the third (Ka Wah Bank in
1985) seems to be related to the failure of Overseas Trust Bank and to that of a
specific foreign borrower. In the first two cases strong negative abnormal returns

What is systemic risk today?

65

occurred for locally listed bank stocks, but the evidence provided on rational
investor reactions differentiated according to exposures seems to be rather inconclusive.
In terms of the concept developed above this literature shows weak systemic
events in the narrow sense, since stock price fluctuations do not imply failures.
4.1.3

Analyses of deposit flows

Another test of contagion measures the reaction of depositors (wholesale andretail) to “bad news.” If in response to problems revealed about a bank (or a groupof banks) i depositors also withdraw funds from another bank j, there is evidenceof a contagious bank run.
Saunders (1987) examines whether two key announcements about the shapeof Continental Illinois Bank in April and May 1984 had any discernible effect onother banks’ US or overseas deposits. The April 18th announcement of a US$ 400
million increase in Continental’s problem loans seemed to have no effect on US
deposits, while the May 10th “denial of rumours” by the US Office of the Comptroller of the Currency (OCC) seems to have triggered “flight to quality” (i.e.
shifts to safer banks and more secure deposits) by large US banks but not a general run. The total of non-sterling deposits at either American, Japanese or otheroverseas banks in London did not decline in April or May (but risk premia onthese deposits generally increased, see section 4.1.4 below).
Saunders and Wilson (1996) study the deposit flows of 163 failed nationalbanks and 229 surviving banks in the United States during the Great Depression(1929 through 1933). They find that in the sub-period 1930-32 there is evidenceof both “pure” contagion, defined as significant withdrawals from institutions
which in the end turned out to be healthy, as well as “informed” withdrawals frominstitutions which appeared already unhealthy before the crisis. While recognising
the presence of “pure” contagion, the authors point out that “uninformed” withdrawals have not been more important than “informed” withdrawals.
Calomiris and Mason (1997) examine the June 1932 Chicago bank panic
during the Great Depression. They group their sample of 114 Chicago banks into
3 categories: non-panic failures, panic failures and survivors. Statistically significant deposit withdrawals from the 62 survivors, which are only weakly smaller
than those from the 28 panic failures, indicate the presence of contagion due toasymmetric information regarding individual banks’ solvency situation. The
authors further ask whether these contagious withdrawals led to contagious
failures or whether the failures observed were rather those of relatively weakbanks in the face of a common asset price decline. To that end they apply a logit
estimation of “ex-ante” failure probabilities (based on balance-sheet data) for
these groups, either including panic failures, or excluding them. Since in bothcases panic failures received a higher predicted failure probability than survivors,
the authors conclude that only already ex ante weaker banks actually failed during
the panic, which is consistent with the hypothesis that “pure” contagious failures

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did not occur. They explain this finding with the existence of private cooperative
arrangements among banks.
4.1.4

Examinations of bank debt risk premia

Some work has been done to see whether contagion effects can be detected in themarket prices of bank debt instruments. Carron (1982, Table 1) shows that theFranklin National failure in New York (and perhaps also the Herstatt failure in
Germany) in mid-1974 led to an increase in the quarterly average spread between
US “jumbo” certificates of deposits (CDs) and 3-month Treasury bills by a factor
of at least six, which is consistent with contagion via risk premia. Giddy (1981)
argues that bid rates for Eurodollar deposits of 30 banks in London during Julyand August 1981 varied only very little between individual banks and that thedifferentials were hardly related to proxies of individual bank or country risk.
Saunders (1986) computes correlations of interbank rate risk premium indices forthree different country groups before and after the start of the 1982 debt crisis. He
observes statistically significant increases of the correlation of risk premia between industrial countries and middle-income LDCs and between middle income
and low-income LDCs, which he considers to be consistent with contagion between those two groups of countries. However, in a follow-up study (Saunders,
1987) he derives that the correlation of risk premia between industrial countries,
non-oil exporting LDCs and countries with debt re-scheduling was actually lower
in the “crisis period” 1974 through 1978 than in the “non-crisis period” 1979
through 1983, so that “there appears to be no evidence of contagion in the crisis
period” (p. 215). In any case, the correlations approach cannot distinguish between systematic shocks and contagion, as defined in the conceptual section
above (Section 2).
Karafiath et al. (1991) undertake an event study of the effect of the 1987
Brazilian debt moratorium on bond prices of 22 US bank holding companies (allwith country exposures to Brazil). In contrast to the equity price reactions reported in the previous section, the cross-section of weekly bond yields in excess ofTreasury note yields were far from being significantly abnormal. One interpretation of their differential results between equity and bond returns is that the market
expected that those banks would earn lower profits (and therefore pay less dividends) due to the debt crisis but that none of the bank holding companies would
actually default on its debt. Finally, Jayanti and White (1996) estimate statisticallysignificant increases in the average certificate of deposit (CD) rates—at constant
Treasury bill reference rates—for both UK and Canadian banks after the Continental Illinois failure in the United States in May 1984. In their case this result is
consistent with the international contagion effect visible in equity returns mentioned in the previous section. Saunders (1987, fn. 28) also acknowledges that the
average spread between 3-month Euro-dollar deposits and T-Bills doubled during
the Continental Illinois problem months of April and May, which again is consistent with international systemic risk in the weak sense. An even stronger effectWhat is systemic risk today?

67

was visible in the average monthly domestic risk premium, as measured by thedifference between 3-month CD rates and 3 month T-Bill rates, which more thantripled during April and May (Saunders, 1987, fn. 27).
The evaluation of the event study approach applied to risk premia in debt rates,
as a test for contagion effects is, of course, similar to the application to equity
returns.
4.1.5

Measurement of effective exposures

A last approach is to directly measure whether exposures to certain (potentially or
effectively failing) banks are larger than capital. While prudential rules limiting
large exposures should usually prevent banks from lending more than a small
share of their capital to a single borrower, very large exposures can occur temporarily vis-à-vis “core institutions,” namely large clearing banks.
Kaufman (1994) reports some results from the US inquiry into the Continental
Illinois case, one of the “core institutions” at the time. Shortly before the failure,
65 financial institutions had uninsured exposures in excess of their capital to thebank. It was estimated by the Congressional study that, if Continental’s losses had
been 60 per cent (i.e. creditors would lose 60 cents of every dollar lent), then 27
banks would have been legally insolvent and 56 banks would have suffered losses
above 50 per cent of their capital. The actual losses of Continental finallyamounted to below 5 per cent, so that none of its correspondents suffered solvency-threatening losses. Michael (1998) reports some effective exposures from
London interbank markets.
This approach is strongly linked to empirical research on the impact of failures in payment and settlement systems, which we survey in section 4.3 below.

4.2

Evidence on contagion in financial markets

In the recent past some evidence has been accumulated that contagion phenomena
can also occur among financial markets. We focus here on the contagion acrossmarkets (section 3.2.1 above). Although there is potentially a large literature on
international financial integration, our review is relatively selective since financial integration in itself does not imply contagion. We only report evidence that
support our definition of contagion, namely the existence of spillover effects
across securities markets that are not justified by fundamentals and operate differently in “crisis periods” than in “normal times.” We present four types of contributions: (i) return correlation across markets, (ii) volatility spillover effects, (iii)
the analysis of the dependence of extreme price deviations across markets, and(iv) event studies of the determinants of currency crisis. These different approaches are complementary and some papers cover them jointly. In addition,
they rely, to a large extent, to the same analytical tools, namely GARCH modelling, in the wake of the findings that most financial series exhibit autoregressive
conditional heteroscedasticity.

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4.2.1

Correlation across markets

The first type of tests measuring contagion is simply based on the correlation of
returns across markets. The main stylised fact is that correlation increases whenmarkets are more volatile, hence reducing the completeness of financial markets
and the gain from international diversification. This may undermine the stabilityof financial institutions. Evidence is based on contemporaneous as well as lagged
correlations.
4.2.1.1

Contemporaneous correlation

As indicated above, contemporaneous correlation does not directly measurecontagion, which, in principle, would require studying the transmission of shocks
over time. However, in securities markets the speed of transmission of a large
systematic shock may be such that the propagation of the disturbance may bealmost instantaneous. In addition, the econometrician may be not able to use data
at a sufficiently high frequency, if she or he wants to control for changes in fundamentals. Finally, the allocation of risks by securities markets may worsen andtherefore have systemic consequences if, on certain occasions, the correlation
between individual securities markets increases. In that area of research, there issubstantial evidence on equity markets following the 1987 stock market crash.
In a seminal paper, King and Wadwhani (1990) regress daily equity returns in
London and New York on each other and show that during the period from 19
October to 30 November 1987 the correlation between returns on the FTSE-100
and the Dow Jones was significantly positive, while it was not significantly
different from zero during the rest of the year. In a more systematic fashion, King,
Sentana and Wadwhani (1994) extend the analysis to monthly returns on 16 stock
markets during the period January 1970 to October 1988, assuming that theinnovations on equity returns follow a multivariate GARCH (1,1) process which
depends on observable macroeconomic “observable” as well as “unobservable”
components. Their finding is that only a small proportion of the covariance
between national stock markets can be accounted for by “observable” economic
variables. While the “unobserved” components might include omitted variables,
they can also reflect market sentiment and contagion. In particular, it appears thatthe observed factors fail to explain the substantial increase in correlation during
the 1987 crash. The authors also show that the apparent upwards trend of theequally weighted average of conditional correlations between the national excess
equity returns may actually be explained by a simple dummy variable accounting
for the 1987 stock market crash.
4.2.1.2

Leads and lags between securities markets

In a study corresponding very closely to our definition of contagion in securities
markets, Malliaris and Urrutia (1992) run causality tests on daily closing returnsfor 6 major stock market indexes (SP 500, Tokyo Nikkei, London FT-30 andWhat is systemic risk today?

69

other Asian markets) from May 1987 to March 1988, taking into account differences in time-zone trading. Practically no lead-lags are uncovered for the pre- andpost-crash periods, but important unidirectional as well as feedback relationships
are found during the October 1987 crash. The results also provide evidence of the“passive” role of Tokyo but fail to confirm the leading role of New York duringthat period.
Lin et al. (1994) qualify King and Wadwhani’s (1990) analysis, using intraday equity returns in order to account for differences in time zone trading. They
divide close-to-close returns into close-to-open and open-to-close returns andargue that for two markets without overlapping trading periods, a test of contagion should be based on the existence of a significant lagged correlation between
daytime (Open-to-Close) returns in the two countries. Under the hypothesis ofmarket efficiency, news revealed in the foreign market in daytime (Open-toClose) or overnight (Close-to-Open) is completely incorporated into the opening
prices so that the Open-to-close return should not be affected. They report that
contemporaneous correlation between foreign daytime (Open-to-Close) anddomestic overnight (Close-to-Open) returns was much smaller around the crash,while the correlation between foreign daytime returns and subsequent domestic
daytime returns rose around the crash. One possible explanation is that traders
took more time to figure out the implications of a sharp decline in prices. Lin and
Ito (1995) also found that for the period October 1985 to December 1991 andconsidering the Tokyo Nikkei and the New York S&P index, the contemporaneous effect of the foreign daytime return on the domestic overnight return is statistically significant, whereas the lagged effect of the foreign daily return on thedomestic daily return is insignificant, once lagged effects of home return aretaken into account. Such a result provides evidence in favour of international
efficiency and against contagion, although the introduction of the lagged home
return in the equation indicates that domestic markets may not be fully efficient.
In addition, the authors are unable to provide significant evidence in favour of aneffect of trading volume—which measures heterogeneity of information and thecontagion of investors’ sentiment—on the international correlation of equity
returns. During the 1987 crash period, however, the coefficients on lagged spillover effects are much more significant and contemporaneous correlation lesssignificant, in particular from Tokyo to New York, indicating that news revealedin the foreign markets could not be incorporated in the opening price due toheightened uncertainty.
4.2.2

Volatility spill-over effects across markets

We survey now the different contributions that have attempted to measure volatility spillover effects across markets to shed light on possible contagion. Following
the discussion in section 2.2.2, it is however necessary to stress that volatility canbe predictable as a result of the fact that the arrival rate of news is correlated overtime. Volatility spillover effects may also be explained by responses to changes in70

Oliver De Bandt and Philipp Hartmann

common fundamentals. Against this background, a drawback of that literature isthat focusing on high frequency data (daily or intra-daily) there is no room for a
direct measure of macroeconomic determinants, apart from the effect of unexpected “news.”
Similarly to the analysis of correlation reviewed in section 4.2.1, this literature which has developed since the late 1980s / early 90s, first attempted to findevidence of more significant transmission of volatility during the 1987 stock
crash. In particular, Hamao, Masulis and Ng (1990) study intra-daily returns onequity in Tokyo, London and New York. Open-to-close returns are measured as a
GARCH (1,1) process and the authors test whether the conditional variance ofinnovations may be explained by volatility surprises in the foreign market. Surprises are measured by the squared residual derived from the foreign market that
trades the most recently (i.e. Tokyo for London, London for New York and New
York for Tokyo). Using observations on the 1985-1988 period, they show that theforeign volatility has a significant effect only when the post-October 1987 period
is included. Lin et al. (1994) provide a little more formal structure to the arrival ofnews and decompose the unexpected return in the foreign market into a local anda global factor. However, they are unable to distinguish between “shocks tointernational fundamentals” and “internationally contagious psychology.” Investors solve a signal-extraction problem in order to uncover the two types of shocks
affecting the foreign return, since only the global factor may create a spillover
effect on the domestic market. The authors find that the signal extraction model
provides a better fit to the Tokyo overnight return data than a simple GARCH-in
mean, especially when the 1987 crash is included in the sample period. However,Susmel and Engle (1994), using hourly data on equity markets, conclude that
there is no strong evidence of spill-over effects for the period including the 1987
crash: spill-over effects seem to be limited to the opening hour of the trading
period.
As new observations have become available, subsequent works have addressed the more general question of asymmetric effects in the transmission ofvolatility. Koutmos and Booth (1995) investigate daily open-to-close returns fromMarch 1986 to January 1993 in Tokyo, London and New York. They assume thatthe three markets open sequentially and that return innovations follow an exponential GARCH process, which allows the size as well as the sign of the shocks to
be distinguished. Their finding is that volatility spill-over effects are more pronounced when the news arriving on the last market to trade is bad (i.e. when
standardised return innovations are negative). Kanas (1998) finds comparable
results when applying the same methodology to a sample of European stocks(London, Paris and Frankfurt) for the period 1984-1993, using close-to-close
daily returns.
To our knowledge, only a limited number of studies have attempted to investigate volatility spill-over effects across other types of assets since the seminal
paper by Engle et al. (1990). These authors concluded that volatility in foreignexchange markets was not an isolated phenomenon affecting a given currency (aWhat is systemic risk today?

71“heat wave”), but a global issue (akin to a “meteor shower”). However, suchanalysis did not address the origin of such a feature, namely whether it corresponds to correlated fundamentals or a failure of a strong form of market efficiency and did not investigate the robustness of the transmission channel when markets are more volatile. One should also note that until 1994, the conclusion of theliterature was that bond markets were not characterised by excess volatility, sothat volatility spill-over effects seemed pointless. In contradiction with the latter
view,33 Borio and McCauley (1994) use indicators of implied volatility derived
from option prices in order to test whether volatility spill-over effects—measured
by the regression coefficient between pairs of countries—are more pronounced
during periods where volatility is high. As their equations also include an autoregressive term measuring volatility persistence, the authors are able to conclude
that the coefficient of the spill-over effect is effectively larger in a period of highvolatility, but that its effect dies out more quickly.
4.2.3

Dependence of extreme price deviations across markets

The first attempts to measure the dependence between extreme price deviations
were indirect and based on the study of conditional correlation between asset
returns.34 Recent applications of “extreme value” theory (Embrechts et al., 1997)
to financial markets have focused on the correlations between the tails of the
distribution of returns in equity and exchange markets. Consistent with our concept of systemic risk, the intuition is that economic agents are more interested inestimating “extremal dependence” rather than statistical dependence for the whole
distribution. Another methodological issue is that no correlation does not imply
independence when returns are not normally distributed as is usually the case forasset prices with fat tails. Using daily data on equity and currency returns in G7
countries, Straetmans (1998) computes the conditional probability that two financial markets crash simultaneously (i.e. that they jointly exhibit excess returns
above a certain threshold) given that at least one of the two markets experiences alarge deviation. For currency markets, where a threshold of 5% is taken to measure large deviation, there is significant dependence in the tails. In addition, conditional crash probabilities seem to be much higher under free float than under atarget zone. Regarding stock returns, apart from high linkages between the US
and Canada as well as between France and Germany, market contagion seems tobe very weak. One explanation of this result is that spillover effects are not si33
Rodrigues (1996) who studies the determinants of the volatility of equity and bond returns,
shows that observed macroeconomic variables explain a less significant part of the variability in theconditional variance of bonds in the US and Canada than in other countries.
34
A few studies have investigated whether large deviations in equity returns affected thecorrelation across markets. Longin and Solnik (1995) conclude that the correlation between equity
returns rises during periods of high volatility in the US market. Karolyi and Stulz (1996) provide
evidence that large shocks to the overall market indices increase the return correlation. De Santis
and Gerard (1997) find that during “bear” markets US equities are more correlated with the “World”
portfolio than during other periods. Borio and Mc Cauley (1996) show that the cross correlation ofbond yield volatility tended to increase during the periods of market turbulence in 1994.

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multaneous, in particular due to the existence of different trading hours, so thatthe crash probability is downward biased.
4.2.4

Event studies of the determinants of currency crisis

With a view to measuring contagion in currency markets, Eichengreen et al.
(1996) investigate an original panel of 20 industrial countries for the period 19591993. They estimate a binary probit model, where the explained variable is aquarterly index of exchange rate pressures. The authors test whether a crisis
elsewhere in the world has any explanatory power. They provide evidence suggesting that, even controlling for political and economic fundamentals, a crisis
elsewhere in the world increases the probability of a speculative attack by aneconomically and statistically significant amount of 8 percentage points. Although this constitutes one of the most consistent measures of contagion, one may
wonder whether the quarterly horizon is really appropriate for testing contagion
across currency markets and whether one should not use higher frequency data.
Finally, Glick and Rose (1998) show that currency crises tend to be regional due
to trades linkages, although as indicated above, this is not “pure” contagion, butreflects changes in fundamentals.
To conclude, the finance literature provides some evidence in favour of contagion in securities markets. However, due to the lack of a coherent theoreticalmodel of transmission in securities markets, the literature fails to address the issue
in a convincing way. Models of signal extraction have been suggested but theunderlying definition of “news” remains unsatisfactory. In addition, evidence isgenerally provided for contagion within the same class of assets (e.g. equity orbonds markets) while the cross-asset dimension (i.e. spill-over effects from equity
to bonds and currency markets) is ignored. Finally, contagion is usually investigated across industrial countries or some emerging countries, while the analysis
of contagion between these two sets of countries remains to be done.

4.3

Evidence on contagion in payment systems

Published empirical studies about the importance of systemic risk in payment
systems are very rare. To our knowledge, there are only three rigorous analyses ofit, which all apply a simulation approach to examine the scope for contagion
effects in large-value interbank net payment systems.
Humphrey (1986) simulates the potential effects of a major participant’s
failure in the US CHIPS by “unwinding” all the transactions involving such aparticipant on two randomly selected business days in January 1983. When thisevent rendered another bank’s net debit position larger than its capital this bank’stransactions were also cancelled due to “insolvency,” and so on. This simulationsuggested that a large share of all CHIPS participants could default (around 37
percent), with a high value of deleted payment messages. Also, Humphrey findsthat the institutions affected by the initial failure were quite different between thetwo days examined.

What is systemic risk today?

73

In a very careful study, Angelini et al. (1996) apply a substantially generalised
simulation exercise to the Italian net settlement system, considering end-of-day
bilateral net balances for all 288 participants during January 1992. Basically, theauthors generate frequency distributions of defaults, eliminated payments, etc. byletting each system member alone fail once per business day. From these simulations, the systemic risk in the Italian settlement system seems to be lower thanthat for CHIPS (on the basis of a comparison with Humphrey’s (1986) results).
Recorded chain defaults involved on average less than 1 per cent of system participants and never more than seven banks. The share of participants potentiallytriggering a systemic crisis amounted to 4 per cent of the total, and the “suspects”
did not change a lot over time (many of them being foreign banks).35
McAndrews and Wasilyew (1995) undertake a similar study of systemic riskin net systems with unwinding provisions based entirely on Monte Carlo simulations. In each run the number of system participants and their bilateral payments
are drawn from random distributions. Then the participant with the largest overall
net debit position is made to fail on all its payment obligations. It turns out thatsystem-wide repercussions of such a failure increase with the average size ofbilateral payments, the number of system participants and with the degree of“connectedness” between the participants (as measured by the likelihood that any
two banks exchange payments).
One advantage of this type of simulation approach to payment system risk is
the quantitative measurement of the extent of contagion and its very practical
implications, in particular when real payments data are considered. It can beobjected that this approach does not allow for reactions of other payment system
participants to initial failures and might therefore somewhat overstate contagion
risk. Moreover, nowadays many net payment systems have reduced or removed
potential unwinding of transactions for exactly the reason that they might enhancesystemic risk. Most other evidence of systemic problems in payment (and settlement) systems seems to be of rather anecdotal nature, such as that described in thecontext of the 1987 stock market crash (see, for example, Brimmer, 1989, andBernanke, 1990).

5

Conclusions

In this paper we discussed the various elements of systemic risk with a view to,
first, developing a broad concept of this risk, which underlies the understandingof financial crises and which can be used as a baseline for financial and monetary
policies to maintain stable financial systems. We argue that a comprehensive viewof systemic risk has to integrate bank failure contagion with financial markets
spill-over effects and payment and settlement risks. At the very basis of theconcept (in the narrow sense) is the notion of contagion—often a strong form of
35
The largest individual worsening of a net position was 18.5 times capital (as compared to 32.4
times capital in Humphrey (1986)).

74

Oliver De Bandt and Philipp Hartmannexternal effect—working from one institution, market or system to the others. In a
broad sense the concept also includes wide systematic shocks which by themselves adversely affect many institutions or markets at the same time. In this sense,
systemic risk goes beyond the vulnerability of single banks in a fractional reserve
system.
We reviewed the quantitative literature in the light of our concept of systemicrisk and identified a number of important gaps, which appear worthwhile fillingin future research. Rigorous theoretical models of interbank contagion only
started to be developed, for example, regarding the interaction between asymmetric information and physical exposure—two crucial elements in potential propagations. Models linking banking and financial markets, as well as payment/settlement systems are simply nonexistent. The overwhelming part ofeconometric tests for bank contagion effects is limited to data for the UnitedStates. Event studies of bank equity returns, debt risk premia, deposit flows or
physical exposures for European, Japanese or emerging market data are rare or
virtually absent. Some more recent event studies of bank failures based on equity
returns indicate that weak systemic events were in proportion to bank exposures,
whereas there is some historical evidence of “pure” contagion during US banking
crises.
Similarly, while there are numerous studies about the correlations of asset
prices in general, the evidence about cases where one market crash causes anothermarket crash is much more limited. Where those financial market contagion
studies exist, they mainly look at contagion within the same asset class without
considering potential contagion (or “flight to quality”) to other asset classes andthey fail to achieve the difficult task of identifying “pure” contagion effects as
opposed to the efficient adjustment of market prices. Finally, empirical analysesof contagion effects in payment and settlement systems seem to be limited to net
payment systems, widely ignoring securities settlement systems or “network
externalities” potentially resulting from “gridlock” situations in gross payment
systems.
Overall, we feel that the recent financial crises (Nordic banking crises, Mexico, East Asia, Japanese banking crisis, Russia, Brazil, etc.) sufficiently underline
the importance of understanding systemic risk as a tool in defining policies andencouraging market initiatives aiming at financial stability. It was not our objective to explain any of these crises in themselves. If we succeeded in convincing
some researchers to try filling some of the gaps we identified regarding more
fundamental issues, which could then help explain and prevent real crisis situations, then we have achieved our objective.

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