Government and Opposition, Vol. 41, No. 4, pp. 581–588, 2006

Review Article
Arthur Spirling and Iain McLean: The Rights and Wrongs of Roll
Calls
Keith T. Poole, Spatial Models of Parliamentary Voting, New York and Cambridge, Cambridge University Press, 2005, in Analytical Methods for Social
Research series, 248pp., hardback, £40.00, ISBN 0-5218-5194-7; paperback,£15.99, ISBN 0-5216-1747-2.
Keith Poole’s Spatial Models of Parliamentary Voting introduces readers to theremarkable progress that studies of parliamentary voting have made in the
United States, compared to their much more modest progress elsewhere.
Poole’s book is an advanced manual, which may lose many readers of thisjournal by pp. 11–12, when he states without explanation that voters’ utility
functions in political issue space are probably Gaussian exponential response
functions. However, we would encourage readers to persevere, because thisbook is important both for what it says and for what it does not say, and bothfor its successful claims and for its unsuccessful claims. We begin by introducing the history of roll-call analysis before Poole.

THE ORIGINS OF ROLL-CALL ANALYSIS IN IOWA AND ROCHESTER
Roll-call analysis is simply the analysis of recorded votes in a legislature (‘rollcalls’ in US terminology). As explained below, this science is far advanced in(and in relation to) the USA. In particular, every roll-call vote ever takenin the more than 200 years’ history of the House of Representatives is
now available online, together with software written by Poole and his collaborators to interpret and classify the data. This is a truly monumental
achievement.
Roll-call analysis has been applied a little bit to other legislatures, including to the Parliament of the French Fourth Republic and the European
Parliament. Apart from a few brave forays, it has been little used to study rollcalls in either house of the British Parliament. This is partly a data problem;
partly an attitude problem; and partly a deeper intellectual problem. The
data problem is that machine-readable roll calls for the House of Commons
exist only for the Parliaments of 1841–47 and from 1992 to the present day.
For the House of Lords they are only now being developed in conjunction© The Authors 2006. Journal compilation © 2006 Government and Opposition Ltd
Published by Blackwell Publishing, 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main
Street, Malden, MA 02148, USA.

582

GOVERNMENT AND OPPOSITION

with the House authorities. That said, David Firth, with one of the present
authors, has written a program in the statistical language and environment R
that, in theory, would allow the conversion of paper copies of Hansard toelectronic voting records via a high-resolution document scanner. The attitude problem is that many historians and political scientists are unskilled instatistics and afraid of numbers and/or of computing. These problems aretractable. But there is a deeper problem, as we aim to show in this review
article.
Poole’s book says little about the early history of roll-call analysis andalmost nothing about its founder, W. O. Aydelotte (1910–96). After a degree
in Classics at Harvard and a PhD in History in Cambridge under the intimidating Herbert Butterfield, Aydelotte worked in the University of Iowa from1947 for the rest of his life. He ‘transformed a department of modest reputation into an exciting intellectual environment, while at the same time
pioneering new modes of research and analysis in his field of history’.1
Aydelotte was to quantitative history as, in the next generation, William Riker
was to be to analytical political science. Both were great institution builders,at Iowa and Rochester respectively; both spread their disciples around an
entire discipline.
Aydelotte was a great Anglophile. His choice of the UK Parliament of1841–47 for his life’s work was inspired. The repeal of the Corn Laws in 1846
was one of the cataclysmic events in British parliamentary history. Prime
Minister Sir Robert Peel had been elected in 1841 with a secure partisan Tory
majority. His support base lay in agriculture and the Church of England.
Both of them had a material interest in protection – against grain imports
and against other religions, respectively. Peel defied both. In 1846 herepealed the protectionist Corn Laws with the support of almost all the
Opposition and only a third of his own party. Peel’s contemporaries (including not only Richard Cobden but also Karl Marx and Friedrich Engels)recognized this as a revolutionary move, which ushered in the era of freetrade imperialism. It also destroyed the Tory Party until 1874. Every succeeding Conservative leader at times of crisis has announced that he will not dowhat Peel did ( just as every Labour leader in crisis announces that he will not
do as Ramsay MacDonald did).
Aydelotte coded all the principal roll calls in the House of Commons of
1841–47 – 186 divisions in all. For each of 815 MPs who served in thatparliament, he coded his vote on all 186 divisions, and added contextual

1
Allan G. Bogue and Gilbert White, ‘William Osgood Aydelotte, September 1,
1910–January 17, 1996’, in National Academy of Science, Biographical Memoirs 73,
Washington, DC, National Academy Press, 1998, pp. 40–63. All facts about Aydelotte
are either from this source or from personal acquaintance.

© The Authors 2006. Journal compilation © 2006 Government and Opposition Ltd

REVIEW ARTICLE

583

information about the MP’s party, constituency, education, career andwealth. The result is an 815 ¥ 300-cell data matrix that until recently was little
used.2 To impose order on this mass of data, Aydelotte used Guttman scaling,which he learnt from his social scientist colleagues at Iowa in the mid-1950s.3
He produced no fewer than 21 scales, one of which (‘the Big Scale’) successfully scaled both most MPs and most of their votes, revealing a predominantly
single-dimensional spatial world in which attitudes to Ireland, the established
Church, and the Corn Laws were grouped together. There were some subsidiary dimensions orthogonal to the Big Scale – factory regulation was one– and one set of motions that Aydelotte could scale but not interpret – theMiles’s motions scale. We return to Miles’s motions below.
Keith Poole was a graduate student under the other great institutionbuilder, Bill Riker, and in all his work, including this book, he pays homage
to his mentor (p. xv). Riker’s Rochester School has many classrooms. Riker
himself was most interested in multidimensional politics and the possibilities
of chaos (in the social choice sense). Where there is chaos, any outcome ispossible, and there is no stable equilibrium in majority rule. However, Pooleand his long-time collaborator Howard Rosenthal have focused rather on the
low – mostly single – dimensionality of voting in the US Congress. In theirhighly influential book Congress: A Political-Economic History of Roll-Call Voting
they argue that on only ‘two occasions – both before the Civil War – stablevoting patterns break down entirely, and “chaos” results’.4 In the rest ofCongressional history since 1789, Poole and Rosenthal find a stable patternof voting along the main issue dimensions of the day. Their dataset covers allroll calls in the history of the House of Representatives. Their programs
include OC (Optimal Classification) and the NOMINATE family. These dataand programs are freely available, and Poole and Rosenthal are well known2
But see C. Schonhardt-Bailey, ‘The Strategic Use of Ideas: Nationalizing theInterest in the Nineteenth Century’, and I. McLean, ‘Irish Potatoes, Indian Corn andBritish Politics: Interests, Ideology, Heresthetic and the Repeal of the Corn Laws’, in
F. McGillivray, I. McLean, R. Pahre and C. Schonhardt-Bailey, International Trade andPolitical Institutions: Instituting Trade in the Long Nineteenth Century, Cheltenham, Edward
Elgar, 2001, pp. 146–97 and 99–145 respectively; I. McLean, Rational Choice and British
Politics, Oxford, Oxford University Press, ch. 2; N. Schofield, Architects of Political
Change, New York, Cambridge University Press, 2006. A version with new variables
added by McLean and Schonhardt-Bailey is freely downloadable from http://
www.nuff.ox.ac.uk/Users/McLean/index.htm.
3
Bogue and White, ‘Aydelotte’, p. 52.
4
K. T. Poole and H. Rosenthal, Congress: A Political-Economic History of Roll-Call
Voting, New York, Oxford University Press, 1997, p. viii. The two occasions are the ‘Era
of Good Feelings’ in the 1820s, associated with the collapse of the Federalist Party; andthe 1850s, when an alignment based on slavery overtook the earlier economic interestbased alignments in the years leading up to the Civil War.

© The Authors 2006. Journal compilation © 2006 Government and Opposition Ltd

584

GOVERNMENT AND OPPOSITION

for their generosity in helping scholars of other times and places to run their
OC or (W/D)NOMINATE programs on data from roll calls in legislaturesother than Congress.

PARAMETRIC AND NON-PARAMETRIC SCALING METHODS
Guttman scaling has its origins in psychology, where it is used to solicit theextent to which a particular trait (like spatial awareness or narcissism) ispresent in experimental subjects. In a parliamentary context, the idea is totreat each bill that comes up for voting as a statement with which MPs could
agree (and vote ‘aye’) or disagree (and vote ‘no’) and from the responses
work out where the MPs lie on some underlying dimension. For a running
example, suppose the dimension is how ‘socialist’ or ‘conservative’ MPs are,and that there are 10 bills in our study. A strict interpretation of Guttman
scaling would have the researcher a priori rank order the bills, from ‘most
extreme’ (which we label as 10) to ‘least extreme’ (which we label as 1) interms of what an ‘aye’ vote implies for the conservatism of the person thatvotes ‘aye’. So, a bill like ‘this House believes immigration should be morestrictly monitored and regulated’ is ‘less extreme’ than ‘this House believes
all non-white, non-British born citizens should be immediately repatriated totheir country of birth’ because only the most conservative MPs will vote ‘aye’
to the latter. We say a Guttman scale is ‘perfect’ if a person who agrees witha particular bill also voted ‘aye’ on every bill that was less extreme. So, an MP
who votes ‘aye’ on bill number 6 also voted ‘aye’ on all the bills 1 through 5.
In practice, Guttman scaling does not proceed quite like this. First, thescale is almost never perfect: MPs make mistakes when they vote, or factors
other than their own preferences play into their decisions. We call this ‘error’.
Second, rather than identifying to what extent particular bills are indicatorsof conservatism, researchers can simply ‘let the data speak’ by ordering theMPs according to how much they agree with each other, in terms of how they
voted, regardless of the assumed extremism of the underlying propositions.
So, if MP A agrees with – i.e. votes the same way as – MP B on three out of 10
bills, and MP C agrees with A on six out of 10 bills, we see MP A and MP C as
being more similar ideologically than MP A and MP B. It transpires that, when
we know where the MPs lie relative to each other, we can work out how
extreme the bills that separate them (i.e. on which they disagree) are. And
from knowing the extremity of the bills, we can improve how we classify theMPs. Shuffling between these two stages can be automated, and this is almost
exactly what Poole’s OC algorithm does. As many bills and as many MPs are‘correctly classified’ as is possible, such that we cannot move a single MP leftor right (relative to the other MPs) without predicting that they would vote‘aye’ on a bill that we know they actually voted ‘no’ upon.
© The Authors 2006. Journal compilation © 2006 Government and Opposition Ltd

REVIEW ARTICLE

585

The only assumptions we need are that MPs vote sincerely for the option(aye or no) that they like best and that their preferences are symmetric. This
last fact broadly means that MPs can place themselves on the socialist–
conservative dimension at an ‘ideal point’ and that a bill that moves policy,
say, three units to the left of that position is as palatable to them as one thatmoves policy three units to the right. Technically, we say that OC is a‘non-parametric’ technique, which means that we are making deterministic
statements about how MPs will vote: once we have run the algorithm, andhave identified the MPs’ location (and how the bills stack up), we act as if weknow for certain how the MPs stand relative to each other. For various technical reasons, we sometimes want to make probabilistic statements, for which
we need contrasting ‘parametric’ techniques. However, Poole’s colleagues
have used OC rather than a parametric method to analyse roll calls in the
Parliament of the French Fourth Republic, which was more comparable to
the House of Commons than is the US Congress.5

WHY SPATIAL MODELLING WORKS FOR THE US CONGRESS BUTNOT FOR THE HOUSE OF COMMONSThe book under review introduces both non-parametric and parametricmethods. Chapter 3 deals with OC, and Chapter 4 with the NOMINATE
family. The succeeding chapters give the reader practical hints and tips andsuggest methods conducting natural experiments – mostly using parametricmethods, although a development of OC is described on pp. 192–5. It is all
supported by problem and datasets on Poole’s website, so that instructors
wishing to use his material for an advanced course in scaling may freely do so.
This may be regarded as great generosity, or cultural imperialism, or both.
But before readers of Government and Opposition rush to help themselves tothese free goods, they may worry how exportable Poole’s methods are.
Poole’s book is about ‘parliamentary voting’, but it says remarkably little
about any parliament.6 Almost all his examples relate to the US Congress,
where party discipline is notoriously weak, and Congress members are as
likely to vote for their district as for their party. His only reference to the UK
Parliament reports Schonhardt-Bailey’s application of his programs to the5

Howard Rosenthal and Erik Voeten, ‘Analyzing Roll Calls with Perfect Spatial
Voting: France 1946–1958’, American Journal of Political Science, 48: 3 (2004), pp. 620–32.
6
The confusion is partly linguistic. In US English the word ‘parliamentary’ has abroader meaning than in British English. Ever since Jefferson, Americans have used
the word to mean ‘pertaining to the procedural rules of any deliberative body’ – notmerely to Parliament narrowly defined.
© The Authors 2006. Journal compilation © 2006 Government and Opposition Ltd

586

GOVERNMENT AND OPPOSITION

Aydelotte data on the Parliament of 1841, and the spatial map thus generated(pp. 83–5).
In their earlier book, Poole and Rosenthal wrote:
When . . . local concerns give way to a disciplined two-party system, day-to-day roll callvoting is devoid of interest. A stylized description of Great Britain, for example, would
indicate that national elections create a parliamentary majority. . . . [L]egislation isroutinely approved by all members of the majority and opposed by all members of theminority.7

However, in a non-stylized description, roll-call analysis comes into its own
just in the cases where this does not happen – as with repeal of the Corn Laws,
and with the increasingly rebellious Commons of the 1990s and 2000s.
Poole says of his multiple methods for estimating spatial models: ‘They
have one thing going for them, however: They all work’.8 Unfortunately,when applied to the UK House of Commons, they do not. The problem is notjust that most votes are whipped, nor is it that voting is multidimensional. Nor
yet is it that parametric models work better for the Commons than nonparametric, nor vice versa. It is that neither OC nor the NOMINATE family cancope with strategic voting.
We ran the OC program on the MPs and votes in the House of Commonsfor the Parliament of 1997–2001. Although the incidence of rebellions was
lower than in the previous (1992–97) or following (2001–5 and 2005–)
Parliaments, there were enough to make the 1997 Parliament interesting.9
An extract from the resulting rank-ordering of MPs from left to right is in
Table 1 (The full list is available on application to us).
Table 1 shows that OC works very well to classify MPs between parties. It
ranks all (bar one) Labour MPs to the left of the Liberal Democrats, puts all
Scots, Welsh, Irish nationalist and Liberal Democrat members next, then all
Conservatives to their right and the Ulster Unionists of all varieties furthest to
the right. That corresponds to expert survey results – except that someexperts score the Liberals and Scottish and Welsh nationalists to the left ofLabour on some issues. However, the problem in OC is not its between-party
rankings but its within-party ranking of rebels in the governing party. It
reports that the leftmost Labour members in the 1997 Commons were Giles
Radice, Sam Galbraith and Ron Davies; and that the rightmost Labour
members were Tony Benn, Jeremy Corbyn and Bernie Grant. The late Bernie
Grant was apparently so right-wing that he was the only Labour MP, apartfrom the floor-crossing Shaun Woodward, to have some non-Labour
members to his left.
7

Poole and Rosenthal, Congress, p. 3.
Keith T. Poole, Spatial Models of Parliamentary Voting, New York and Cambridge,
Cambridge University Press, 2005, p. 16.
9Philip Cowley, Revolts and Rebellions: Parliamentary Voting Under Blair, London,
Politico’s Publishing, 2002.
8© The Authors 2006. Journal compilation © 2006 Government and Opposition Ltd

587

REVIEW ARTICLE

Table 1
MPs from ‘Left’ to ‘Right’ 1997–2001
Case

Last NameFirst Name

Party

1
2
3
4
5
81
211
409
411
412
415
417
420
422
425
426
431
432
435
458
459
490
492
509
606
634
666
667
668

Radice,Galbraith,
Davies,Turner,Gibson,Blair,
Prescott,
Dalyell,
Marshall-Andrews,
Skinner,
Abbott,Benn,
Corbyn,Livingstone,
Hume,
Grant,
Jones,
Bell,
Salmond,Ashdown,
Kennedy,
Woodward,
Trimble,Heath,
Hague,
Widdecombe,
McCartney,
Ross,
Paisley,

Giles
Sam
Ron
Neil
Ian
Tony
John
Tam
RobertDennisDiane
Tony
JeremyKen
John
BernieIeuan Wyn
MartinAlex
Paddy
Charles
Shaun
David
EdwardWilliamAnn
RobertWilliam
Ian

Lab
Lab
Lab
Lab
Lab
Lab
Lab
Lab
Lab
Lab
Lab
Lab
Lab
Independent
SDLP
Lab
Plaid Cymru
Independent
SNP
LD
LD
Lab
UUP
Con
Con
Con
UKUP
UUP
DUP

Source: Hansard divisions classified using OC (See text).

This is of course the reverse of the truth. The MPs appearing at therightmost extreme of Labour are in fact every Labour whip’s list of the usual
suspects – the habitual left-wing rebels. How can the Poole–Rosenthal programs deliver this result? They assume ‘that legislators have Euclidean preferences defined over some ideological/policy space and that they votesincerely for the alternative closest to their ideal point’.10 The problem
occurs not with the Euclidean preferences, but with the supposition that all
MPs vote sincerely and proximally. They do not: in particular, the official
opposition will reject a government bill in favour of the status quo, even when
the status quo is further from their ideal point than the proposed policy.
Alternatively, rebels on the government side, who can signal their rebellion
10

K. T. Poole, ‘Non-Parametric Unfolding of Binary Choice Data’, Political Analysis,
8 (2000), pp. 211–37, quoted at p. 212.
© The Authors 2006. Journal compilation © 2006 Government and Opposition Ltd

588

GOVERNMENT AND OPPOSITION

only by abstaining or by voting against the government bill, will sometimes
vote strategically for an option that is further from their ideal point than is
the government proposal. You do not have to be an experienced parliamentarian to know this. But experienced parliamentarians are good at devising
motions that will achieve just that – namely, to defeat a government proposalby creating a strategic majority against it. Such a parliamentarian could becalled a ‘heresthetician’ in Riker’s terminology.11 Two examples are Philip
Miles, a West Indian sugar magnate who sat for Bristol, and Benjamin Disraeli. They were both Tory MPs in the Parliament of 1841, who opposed
Peel’s moves towards free trade. Miles’s first motion was ‘an artful motion . . . to reduce the imperial duty to 20s and retain 34s for foreign refinedsugar. . . . It attracted support from both free traders and protectionists andwas carried against the government by twenty votes’.12
Disraeli brought about the fall of Peel by opposing the government’s
proposals for Irish coercion in the summer of 1846. In Euclidean space, weknow that the Tory protectionists led by Disraeli actually favoured Irish coercion – the more the better. But Disraeli crafted a heresthetic majority with
the Whigs, Liberals, and Irish members to defeat the government, and force
Peel to resign, in June 1846 a month after the votes on the repeal of the Corn
Law. That is why Aydelotte could not interpret the Miles’s motion scale.
Neither Guttman scaling, nor any of its successor techniques, can interpret
strategic voting correctly.
For future research, we suggest that political scientists abandon traditional
spatial models and more recent ideological classification techniques for thecase of the United Kingdom or, in fact, any Westminster parliament wherestrategic voting is suspected. It is simply not the case that the results of an OC
analysis can be interpreted as ideological continua in such circumstances.
More general – non-model based – techniques, such as cluster analysis, may
prove more fruitful, and will be explored in future work with colleagues. But
we do not wish to end on a chiding note. There are many legislatures forwhich the Poole family of models work well. They include the US Congress
and the European Parliament. For parliaments in which there is little or no
strategic voting, they mark the future for roll-call research. But if used
incautiously, they can yoke Bernie Grant and Shaun Woodward together inan uncivil partnership.

11
W. H. Riker, Liberalism against Populism, San Francisco, W. H. Freeman, 1982; andhis The Art of Political Manipulation, New Haven, CT, Yale University Press, 1986; I.
McLean, ‘William H Riker and the Invention of Heresthetic(s)’, British Journal of
Political Science, 32 (2002), pp. 535–58.
12
N. Gash, Sir Robert Peel, London, Longman, 1972, p. 447.

© The Authors 2006. Journal compilation © 2006 Government and Opposition Ltd