habits costly investment and current account dynamics abstract we analyze the current account dynamics for a small country model with habit forming consumers and costly investment the model has several empirical and policy implications i it is consistent with stylized facts regarding the effects of productivity shocks and increases in fiscal spending and regarding the savings investment co movement ii the long run effect of a temporary shock on net foreign assets is often opposite to that of a permanent shock iii under strong habit persistence the welfare dynamics are sluggish so that a beneficial tax financed fiscal policy may have a harmful hangover effect on welfare

money capital and real liquidity effects with habit formation the money in utility model is reconsidered in the presence of endogenous labour and habits with standard assumptions about preferences and a policy rule that sets the nominal interest rate by adjusting the growth rate of money the model exhibits superneutrality in the steady state nevertheless habits give rise to real liquidity effects in the short run after an increase in the nominal interest rate employment falls resulting in a fall in capital accumulation and in the short and long term real interest rates the adjustment of the capital stock is non monotonic employment and the short and long term real interest rates may also adjust non monotonically jel classification e22 e52 e58 monnaie capital et effets reels de liquidite quand il y a formation d habitudes on re examine le role de la monnaie dans un modele d utilite quand travail et formation d habitudes sont endogenes dans le cadre des postulats usuels a propos des preferences et d une regle de politique qui definit le taux d interet en ajustant le rythme de croissance de la monnaie le modele fait preuve de super neutralite en regime permanent neanmoins les habitudes entrainent des effets reels de liquiditea court terme apres un accroissement dans le taux d interet nominal l emploi chute ce qui entraine un ralentissement dans l accumulation du capital et une chute des taux d interet reels a court et a long terme l ajustement dans le stock de capital n est pas monotone l emploi et les taux d interet reels a court et a long terme peuvent aussi ne pas s ajuster de facon monotone

a positive theory of social security based on reputation we construct a general equilibrium model in which a pay as you go social security system can be adopted and sustained as a political and economic equilibrium we alalyze the welfare implictions of this system and compare general equilibrium welfare measure to the commonly used notion of actuarial fairness

habit formation interdependent preferences and demographic effects in the almost ideal demand system the authors model myopic habit formation interdependence of preferences among consumers and demographic effects as taste shifters in a micro consumer demand model of the almost ideal demand variety the model is estimated for dutch micro data the authors investigate the dynamic properties of the model and find that it behaves very differently from models without interdependence of preferences the implications for micro macro modeling are discussed copyright 1991 by royal economic society

income elasticities for food calories and nutrients across africa a meta analysis abstract this paper aims to provide a better understanding of the relationship between income and the demand for different types of food nutrients and calories in africa by conducting a meta analysis of income elasticity estimates we build a meta sample consisting of 1523 food income elasticities 369 nutrient income elasticities and 123 calorie income elasticities extracted from 66 primary studies covering 48 african countries the sample displays a large heterogeneity in income elasticity estimates which our meta analysis aims to explain by looking into attributes of the primary studies and characteristics of the countries considered there are significant differences in the size of the income elasticities across food and nutrient groups foods that make up basic diets tend to have lower income elasticities while elasticities are considerably higher for less basic and more aspirational foods the role of methodological attributes of the primary studies in explaining heterogeneity is found to be small overall our results confirm that although income growth in africa will increase food consumption and lead to more nutritionally diverse diets it is also associated with excessive intakes of fats and sugars raising concerns about over in addition to undernutrition this suggests that income based policies can still play a role in the fight against hunger but that targeted programs are needed to promote nutritionally valuable and healthy diets

equilibrium policy in an overlapping generations economy abstract this paper offers a mechanism for reducing the number of stationary equilibria that arise in a simple two period lived overlapping generations economy since each equilibrium is associated with a different combination of monetary and fiscal policies i assume that at each date the agent in his second period of life determines how that period s monetary and fiscal instruments will be set i show that the set of stationary equilibria where this occurs is a proper and nonempty subset of the set of stationary competitive equilibria and that at least one such equilibrium is a pareto optimum

testing the response of consumption to income changes with noisy panel data this paper tests the rational expectations lifecycle model of consumption against i a keynesian model and ii the rational expectations lifecycle model with imperfect capital markets the tests are based upon the relative responsiveness of consumption to income changes that can be predicted from past information and income changes that cannot he predicted the tests allow for measurement error in income the results reject the keynesian model and generally support the lifecycle model but the results are not sufficiently precise to rule out the possibility that some households are liquidity constrained measurement error has a strong influence on the relationship between consumption and income

a time series analysis of representative agent models of consumption andleisure choice under uncertainty this paper investigates empirically a model of aggregate consumption and leisure decisions in which utility from goods and leisure is nontime separable the nonseparability of preferences accommodates intertemporal substitution or complementarity of leisure and thereby affects the comovements in aggregate compensation and hours worked these cross relations are examined empirically using postwar monthly u s data on quantities real wages and the real return on the one month treasury bill the estimated values of the parameters governing preferences differ significantly from the values assumed in several studies of real business models several possible explanations of these discrepancies are discussed

a test of the habit formation hypothesis using household data numerous studies have confirmed the importance of habit formation as represented by a lagged dependent variable in demand analysis although all work to date has been based on aggregate time series data this study uses household level bls interview panel data to test the habit hypothesis an interrelated demand system for seventeen goods is estimated from cross section data and compared with a similar system based on time series data the results show that the habit component is significantly different between the two data sets and much smaller in the cross section data habit effects while not as large in cross section data as time series are still highly significant several explanations are offered concerning why the two sets of estimates differ copyright 1991 by mit press

fiat money as a medium of exchange this paper presents a completely explicit exchange environment in which agents wishing to exchange one type of good for another choose to trade for fiat money which is then traded for the desired goods this exchange pattern is chosen over barter because specified properties of fiat money make this pattern less expensive than the search for a double coincidence of wants although the transaction services of money affect agents utility the model s welfare implications are those of the basic overlapping generations models not those of models with money balances in the utility function copyright 1989 by economics department of the university of pennsylvania and the osaka university institute of social and economic research association

social contracts as assets a possible solution to the time consistency problem this paper presents a new solution to the time consistency problem that appears capable of enforcing ex ante policy in a variety of settings in which other enforcement mechanisms do not work the solution involves formulating a social contract institution or agreement that specifies the optimal ex ante policy the social contract is effectively sold by succesive old generations to successive young generations who pay for the social contract through the payment of taxes both old and young generations have an economic incentive to fulfill the social contract for the old generation breaking the social contract makes the social contract valueless and the generation suffers a capital loss by not being able to sell it for the young generation the economic advantage of purchasing the existing social contract exceeds its price as well as the economic gain from setting up the a new social contract

in kind benefits and household behavior the impact of snap on food away from home consumption abstract supplemental nutrition assistance program snap formerly known as the food stamp program provides in kind benefits that can generally be utilized for food at home fah only according to economic theory snap benefits are fungible with cash for inframarginal households which may allow participants to spend benefits on non fah items however empirical evidence for this theory is mixed this paper exploits an underutilized source of state level variation the early 2000 s recession to determine the impact of snap participation on household food away from home fafh consumption in a difference in difference framework i compare households in high post recession snap growth states to households in low post recession snap growth states the results show that snap participation causes a significant decrease in fafh expenditure and fafh s share of total food expenditure

the habit of giving i introduction habit formation is thought to exert great influence on behavior it has been proffered as a potential answer to questions as disparate as the size of the equity premium abel 1990 optimal purchases of insurance ben arab briys and schlesinger 1996 labor force participation woittiez and kapteyn 1998 the relationship between savings and growth rates carroll overland and well 2000 responsiveness to monetary policy fuhrer 2000 the importance of brand loyalty gupta chintagunta and wittink 1997 and the existence of a gateway effect between alcohol and illegal drug use pacula 1998 yet there is scant discussion in the economics literature about long term habit forming most studies focus on shorter term intertemporal relationships like changes in annual consumption see inter alia naik and moore 1996 dynan 2002 carrasco labeaga and lopez salido 2005 the importance of early influences on later risk taking malmendier and nagel 2007 and motivations for purchasing different goods portolese dias 2004 has been hypothesized yet there is little direct evidence on the long term impact of shocks to behavior early in life particularly in the way that preferences form and evolve one recent exception is the study of bronnenberg dube and gentzkow 2010 who use variation in consumers previous states of residence to show that early exposure to particular brands of package goods affects purchasing behavior decades later charities in particular care about building relationships with their donors and expend a great deal of effort in the pursuit of small gifts with the expectation that they may lead to larger gifts in the future universities seem to be convinced that this strategy is effective and with 8 7 billion raised from alumni in 2008 the stakes are high council for aid to education 2009 the dean of alumni affairs at columbia university stated that it isn t about the dollars and that the purpose of getting young alumni to donate is to create a habit of giving durkin 2005 fundraising professionals agree one consultant explained i would never say that a small gift is not important because it s building that relationship if you don t build those relationships today you may not have their interest when the day comes that they can give those 101 million donations westmoreland 2008 this sentiment was echoed by an expert on senior class giving at the council for advancement and support of education who explained that the goal of these programs is not to raise money but to begin a pattern of behavior ensign 2010 there is scant evidence that this belief is justified while a number of studies have documented a positive correlation between giving when young and giving when older see monks 2003 turner meserve and bowen 2001 this may be driven by a number of factors that have nothing to do with building a relationship this correlation may actually represent spurious state dependence that arises from unobserved heterogeneity like the alumnus s affinity for the school this is contrasted with true state dependence in which a donation in one period affects preferences for donating in a later period while participation rates are a factor in university rankings it seems evident that development officials assume that habit forming in charitable contributions exists and justifies the pursuit of small gifts when alumni are young with the expectation that this will lead to larger gifts in the future these beliefs hinge on the idea that a habit can form by the simple act of making a gift and that the amount given is possibly irrelevant in essence the proponents of this idea believe that giving regularly when young will cause the individual to be in a state of focus for giving when older willing to make a larger gift perhaps because they are accustomed to giving to the charity in each year standard models of habit forming in which the amount given in an earlier period affects a stock variable and the individual incurs disutility from deviating from this level do not account for this phenomenon

a note on economic conditions and alcohol problems this paper reexamines the effect of the business cycle on alcohol consumption using u s state level analysis introduced by rhum ruhm c j 1995 economic conditions and alcohol problems journal of health economics 14 583 603 using an extended panel this analysis finds that ruhm s estimates are biased and inconsistent due to the problem of non stationarity in alcohol consumption and state economic condition time series corrected estimation using logarithmic first differences confirms ruhm s original finding of pro cyclical alcohol consumption but these results unlike ruhm s are robust to sample period

fiat money in a pairwise trading multi good overlapping generations model abstract this paper studies a stationary pure exchange overlapping generations model with a particular kind of randomly generated pairwise trading pattern this model in contrast to the usual overlapping generations models has the following implications as regards existence it is shown that a standard boundary condition on preferences is sufficient to imply the existence of a stationary monetary equilbrium as regards properties of the equilibrium for some specifications my model has a stationary equilibrium in which claims bear a higher rate of return than fiat money it is also proved that this stationary equilibrium is conditionally pareto optimal

seminonparametric estimation of conditionally constrained heterogeneous processes asset pricing applications the overidentifying restrictions of the intertemporal capital asset pricing model are usually rejected when tested using data on consumption growth and asset returns particu larly when additively separable constant relative risk utility is attributed to the representa tive agent this article investigates the extent to which specification error can explain these rejections the empirical strategy is limited information maximum likelihood in conjunc tion with seminonparametric expanding parameter space representations for both the law of motion and utility we find that consumption growth and asset returns display conditional heterogeneity but this fact does not account for rejection of the overidentifying restrictions as might be anticipated from the work of hansen singleton and others using generalized method of moments methods we also find that expansion of the parameter space in the direction of nonseparable utility causes the overidentifying restrictions to be accepted our estimation strategy provides information on the manner in which the restrictions distort the law of motion in particular imposition of additively separable constant relative risk aversion utility causes the conditional variance of consumption growth to be overpredicted the conditional covariance of asset returns with consumption growth to be overpredicted and an equity premium imposition of nonseparable seminon parametric utility causes distortion in these same directions though the distortions are much smaller which is consistent with the outcomes of the tests of the restrictions

a political theory of government debt and deficits in a neo ricardian framework in the presence of different abilities and therefore different bequests some individuals are bequest constrained even in a neo ricardian world such individuals vote for taxes on future generations through the issuance of bonds thereby increasing their current consumption this produces some crowding out of capital reduces wage rates and increases the interest rate as a consequence even unconstrained individuals are no longer indifferent to the size of government debt the paper derives conditions that are conducive to larger debt and deficits when each of the living generations determines current taxes social security benefits and the national debt by majority rule copyright 1989 by american economic association

search nash bargaining and rule of thumb consumers abstract this paper analyses the effects of introducing two typical keynesian features namely rule of thumb rot consumers and consumption habits into a standard labour market search model rot consumers use the margin that hours and wage negotiation provides them to improve their lifetime utility by narrowing the gap in utility with respect to ricardian consumers this margin for intertemporal optimisation has not been studied yet because this class of restricted agents has been mainly used in models with no equilibrium unemployment our approach allows for a deeper study of the effects of shocks on vacancies unemployment hours wages and how they interact as habits increase rot consumers find it optimal after a positive technology shock to negotiate lower hours and higher wages and this mechanism reduces the simulated correlation between the real wage or productivity and total hours to values closer to those obtained empirically thus with the interaction of rot consumers and consumption habits the labour market search model improves significantly in reproducing some of the stylised facts characterising the us labour market

on money as a medium of exchange we analyze economies in which individuals specialize in consumption and production and meet randomly over time in a way that implies that trade must be bilateral and quid pro quo nash equilibria in trading strategies are characterized certain goods emerge endogenously as media of exchange or commodity money depending both on their intrinsic properties and on extrinsic beliefs there are also equilibria with genuine fiat currency circulating as the general medium of exchange we find that equilibria are not generally pareto optimal and that introducing fiat currency into a commodity money economy may unambiguously improve welfare velocity acceptability and liquidity are discussed

the transition to a new inflation rate in models with habit formation abstract the money in utility model is re considered to allow for habit forming preferences in which habits develop over instantaneous utility from consumption and real money holdings an increase in the inflation rate does not affect the steady state level of capital or consumption but reduces the steady state levels of real money holdings and habits the model has important off steady state dynamics

optimal consumption and portfolio policies when asset prices follow a diffusion process abstract we consider a consumption portfolio problem in continuous time under uncertainty a martingale technique is employed to characterize optimal consumption portfolio policies when there exist nonnegativity constraints on consumption and on final wealth we also provide a way to compute and verify optimal policies our verification theorem for optimal policies involves a linear partial differential equation unlike the nonlinear partial differential equation of dynamic programming the relationship between our approach and dynamic programming is discussed we demonstrate our technique by explicitly computing optimal policies in a series of examples in particular we solve the optimal consumption portfolio problem for hyperbolic absolute risk aversion utility functions when the asset prices follow a geometric brownian motion the optimal policies in this case are no longer linear when nonnegativity constraints on consumption and on final wealth are included by these examples one can see that our approach is much easier than the dynamic programming approach

consumption and habits evidence from panel data the purpose of this paper is to test for the presence of habit formation in consumption decisions using household panel data we use the test proposed by meghir and weber 1996 and estimate the within period marginal rate of substitution between commodities which is robust to the presence of liquidity constraints to that end we use a spanish panel data set in which households are observed up to eight consecutive quarters this temporal dimension is crucial since it allows us to take into account time invariant unobserved heterogeneity across households fixed effects and therefore to investigate if the relationship between current and past consumption reflects habits or heterogeneity our results confirm the importance of accounting for fixed effects when analyzing intertemporal consumption decisions allowing for time non separabilities once fixed effects are controlled for and a proper set of instruments is used the results yield supporting evidence of habit formation in the demand system of food at home transport and services

budget balance welfare and the growth rate dynamic scoring of the long run government budget this paper determines conditions under which a reduction in the role of government either through a tax cut alone or together with accompanying expenditure cuts will improve long run government fiscal balance for a ceteris paribus cut in the income tax rate to improve long run government balance the intertemporal elasticity of substitution must exceed unity a tax cut balanced by an expenditure cut is likely to improve the long run balance even if it does not improve the short run balance the relationship between improving the long run fiscal balance and economic welfare is also analyzed

positive arithmetic of the welfare state abstract this paper argues that social security enjoys wider political support than other welfare programs because i retirees constitute the most homogeneous voting group and ii the intragenerational redistribution component of social security induces low income young to support this system in a dynamically efficient overlapping generation economy with earnings heterogeneity we show that for sufficient income inequality and enough elderly in the population a welfare system composed of a within cohort redistribution scheme and an unfunded social security system represents the political equilibrium of a two dimensional majoritarian election social security is sustained by retirees and low income young while intragenerational redistribution by low income young unlike unidimensional voting model our model suggests that to assess how changes in inequality affect the welfare state the income distribution should be decomposed by age groups

the sensitivity of consumption to transitory income estimates from panel data on households we investigate the stochastic relation between income and consumption specifically consumption of food within a panel of about 2 000 households our major findings are 1 consumption responds much more strongly to permanent than to transitory movements of income 2 the response to transitory income is nonetheless clearly positive 3 a simple test independent of our model of consumption rejects a central implication of the pure life cycle permanent income hypothesis the observed covariation of income and consumption is compatible with pure life cycle permanent income behavior on the part of80 percent of families and simple proportionality of consumption and income among the remaining 20 percent as a general matter our findings support the view that families respond differently to different sources of income variations in particular temporary income tax policies have smaller effects on consumption than do other more permanent changes in income of the same magnitude this abstract was borrowed from another version of this item

money capital and redistributive effects of monetary policies abstract this paper examines the redistributive role of expansionary monetary policies for this purpose a physical environment with heterogeneous agents is described to emphasize two frictions one is a within market friction that agents cannot borrow within each market the other is a cross market friction that agents cannot borrow across markets although a contractionary monetary policy is required to eliminate the within market friction as in many previous monetary models an expansionary monetary policy is required to eliminate the cross market friction when both frictions are operational no monetary policy alone can restore efficiency and the second best monetary policy requires the money growth rate to exceed the friedman rule the first best allocation can be achieved by a combination of fiscal policies and the friedman rule

habit formation and intertemporal substitution in individual food consumption individual food consumption data are used to examine three issues first is food consumption linked intertemporally at the individual level second does the association between current and past consumption reflect habit or heterogeneity third what do the estimates imply about the intertemporal elasticity of substitution the authors find that habit matters that controlling for heterogeneity reduces estimated habit effects and that the product of the estimated intertemporal elasticity of substitution and the risk aversion parameter is less than one these results all lead to rejection of time separable specifications of intertemporal consumption behavior copyright 1996 by mit press

conditional pareto optimality of stationary equilibrium in a stochastic overlapping generations model abstract in this paper i describe and analyze a pure exchange overlapping generations model in which endowments and the dividends of an asset in fixed supply are exogeneous and random they follow a finite state markov process it is shown that no stationary allocation is pareto superior to any stationary equilibrium allocation where pareto superiority is defined in terms of the conditional expected utilities agents maximize in the competitive setting the main contribution of the paper is the optimality proof

household choices in equilibrium this paper is an empirical investigation of equilibrium restrictions on household consumption and male labor supply it exploits a simple factor structure rationalized by two assumptions that household allocations are pareto optimal and that the labor market is competitive the paper estimates household preferences and tests how well this parsimonious factor structure represents panel data on married couples and time series data on asset returns most of the estimates are roughly comparable to those found in previous work no evidence against the simple factor representation is found and the intertemporal capital asset pricing model is not rejected copyright 1990 by the econometric society

longitudinal analyses of the effects of trade unions but union members are different from nonmembers in unobserved ways biasing your estimates y ou should make a selectivity bias correction simultaneously determine union status and economic outcomes develop an unobservables model use longitudinal data archetypical comment on virtually any study of the economic effects of umomsm or suitably modified on any other empirical subject

financial intermediation in an overlapping generations model with transaction costs abstract we analyze an overlapping generations economy where agents interact to share liquidity risk we show that a pure exchange economy has excessive trade in equilibrium because agents interact to rebalance their portfolios intergenerational financial intermediaries reduce the number of interactions because agents only transact when they face liquidity needs in the absence of asset risk intermediaries match redemptions with deposits and dividends and never sell assets if the economy is subject to transaction costs the intermediated economy can sustain higher stationary investment and welfare we also find that dead weight transaction costs can increase welfare because it protects banks from interbank arbitrage and dampens the inherent cyclicality of market economies

rational habit formation abstract this paper discusses consumer demand under rational habit formation if consumer tastes change endogenously through habit stocks depending on past consumption the rational consumer will make allowance of the future habit forming effects of current consumption a model with rational habit formation is made formally equivalent to an intertemporal consumer model without habit formation by redefining the cost of consumption and wealth the cost of consumption is obtained by adding the cost of future induced consumption to the rental price of the commodity the extended wealth concept is obtained by subtracting the cost of the initial stocks of habits and the cost of future physically necessary consumption from wealth the paper also investigates the implication of rational habit formation for constructing one period cost of living indices

money and external habit persistence a tale for chaos this paper studies the dynamic properties of a simple monetary economy model with external habit formation in which money is used for transaction motives we show that large enough though reasonable habit can generate deterministic cycles and chaotic equilibria

panel and pseudo panel estimation of cross sectional and time series elasticities of food consumption the case of american and polish data the problem addressed in this article is the bias to income and expenditure elasticities estimated on pseudo panel data caused by measurement error and unobserved heterogeneity we gauge empirically these biases by comparing cross sectional pseudo panel and true panel data from both polish and american expenditure surveys our results suggest that unobserved heterogeneity imparts a downward bias to cross section estimates of income elasticities of at home food expenditures and an upward bias to estimates of income elasticities of away from home food expenditures within and first difference estimators suffer less bias but only if the effects of measurement error are accounted for with instrumental variables

social security as trade among living generations we model u s social security that is legislated endogeneously by living generations specifically we consider the effects of social security on resource allocation and pareto optimality examining which generations gain from social security and whether some generations lose because saving and transfer decisions are made sequentially in the real world we use an infinite horizon overlapping generations framework in which life cycle saving and transfers to the old are determined by living agents we focus on the case in which agents are altruistic but place sufficiently greater weight on own comsumption than on the consumption of agents in other generations so that starting from a steady state without social security living agents would gain utility if consumption were shifted marginally to them from later generations excerpt

informational diversity over time and the optimality of monetary equilibria abstract the temporal realizations of a random state variable in an overlapping generations model create an informational diversity between members of different generations and require a reexamination of the optimality that competitive equilibria might display in such an environment using an optimality criterion that reflects this informational diversity we prove the optimality of competitive equilibrium in a model with a fixed stock of fiat money a single spot market and good endowments that follow a markov process the need for an optimality criterion that incorporates informational diversity is further motivated by studying the same model with the operation of complete contingent commodities markets

habit formation in consumption a meta analysis abstract we examine 597 estimates of habit formation reported in 81 published studies the mean reported strength of habit formation equals 0 4 but the estimates vary widely both within and across studies we use bayesian and frequentist model averaging to assign a pattern to this variance while taking into account model uncertainty studies employing macro data report consistently larger estimates than micro studies 0 6 vs 0 1 on average the difference remains 0 5 when we control for 30 factors that reflect the context in which researchers obtain their estimates such as data frequency geographical coverage variable definition estimation approach and publication characteristics we also find that evidence for habits strengthens when researchers use lower data frequencies employ log linear approximation of the euler equation and utilize open economy dsge models moreover estimates of habits differ systematically across countries

an overlapping generations model with search abstract search is embedded in an overlapping generations model the young participate in a centralized market and then are matched in pairs in a decentralized market the old only participate in the centralized market if the buyer s bargaining power in pairwise trade is close to unity and if the old are risk averse then the golden rule rate of money transfer is positive such risk aversion the pairwise meetings and dependence of the young s saving on the rate of return are necessary for this result

the permanent income hypothesis and the real interest rate some evidence from panel data abstract a test of the permanent income hypothesis in panel data is formulated taking into account both the time series and cross section variation in the rate of return the over identifying restrictions of the theory rejected

a positive theory of social security in many countries social security accounts for a large fraction of the government budget why is this so given that at any point in time the number of recipients of social security benefits is smaller than the number of contributors in the overlapping generations model studied in this paper all individuals currently alive vote on social security in every period in equilibrium the size of social security is larger the greater is the proportion of elderly people in the population and the greater is the inequality of pre tax income within each generation both predictions of the theory are supported by the empirical evidence in cross country data

intertemporal substitution in import demand and habit formation to study non durable import demand we extend previous work done by clarida 1994 and ceglowski 1991 by considering a two good version of the lifecycle model in which we introduce time non separability in the households preferences the model is estimated using quarterly data for the usa and france using the information contained in the observed stochastic and deterministic trends we derive a cointegration restriction used to estimate curvature parameters of the instantaneous utility function the remaining parameters are estimated in a second step by gmm the constancy of the different parameters is investigated in both the long and the short run habit formation turns out to be an important factor of import demand c 1998 john wiley sons ltd