¹ Poole, Keith A. and Rosenthal, Howard, Congress: A Political-Economic History of Roll Call Voting (Oxford: Oxford University Press, 1997)Google Scholar.

² I will use the terms ‘party cohesion’ and ‘party discipline’ as synonymous in this Note, even though there are good reasons to distinguish between them; see Bowler, Shawn, ‘Parties in Legislatures: Two Competing Explanations’, in Russell J. Dalton and M. P. Wattenberg, eds, Parties Without Partisans (Oxford: Oxford University Press, 2000), pp. 157–179Google Scholar; and Hazan, Reuven Y., ‘Introduction: Does Cohesion Equal Discipline? Towards a Conceptual Delineation’, Journal of Legislative Studies, 9:4 (2003), 1–11CrossRefGoogle Scholar. This allows me some variation in the terms used and eschews the question of what the cohesion scores actually measure. Since I focus on these scores in this Note, how cohesion is maintained is only indirectly, though importantly, relevant for the arguments that follow.

³ E.g., Loewenberg, Gerhard and Patterson, Samuel C., Comparing Legislatures (Boston, Mass.: Little, Brown, 1979)Google Scholar; Harmel, Robert and Janda, Kenneth, Parties and Their Environments: Limits to Reform (New York: Longman, 1982)Google Scholar; Bowler, Shaun, Farrell, David M. and Katz, Richard S., eds, Party Discipline and Parliamentary Government (Columbus: Ohio State University Press, 1999)Google Scholar; Depauw, Sam, ‘Government Party Discipline in Parliamentary Democracies: The Cases of Belgium, France and the United Kingdom in the 1990s’, Journal of Legislative Studies, 9:4 (2003), 130–146Google Scholar; and Depauw, Sam and Martin, Shane, ‘Legislative Party Discipline and Cohesion in Comparative Perspective’ (paper presented at the ECPR Joint Sessions of Workshops, Granada, 2005)Google Scholar.

⁴ E.g., Bartels, Larry M., ‘Constituency Opinion and Congressional Policy Making: The Reagan Defense Buildup’, American Political Science Review, 85 (1991), 457–474CrossRefGoogle Scholar; and Levitt, Steven D., ‘How Do Senators Vote? Disentangling the Role of Voter Preferences, Party Affiliation, and Senator Ideology’, American Economic Review, 86 (1996), 425–441Google Scholar.

⁵ E.g., Attina, Fulvio, ‘The Voting Behaviour of European Parliament Members and the Problem of the Europarties’, European Journal of Political Research, 18 (1990), 557–579CrossRefGoogle Scholar; Bay Brzinski, Joanne, ‘Political Group Cohesion in the European Parliament, 1989–1994’, in Carolyn Rhodes and Sonja Mazey, eds, The State of the European Union, Vol. 3 (London: Longman, 1995), pp. 135–158Google Scholar; Voeten, Erik, ‘Clashes in the Assembly’, International Organization, 54 (2000), 185–215CrossRefGoogle Scholar; Hix, Simon, Noury, Abdul and Roland, Gérard, ‘Power to the Parties: Cohesion and Competition in the European Parliament, 1979–2001’, British Journal of Political Science, 35 (2005), 209–234CrossRefGoogle Scholar; Hix, Simon, Noury, Abdul and Roland, Gérard, Democracy in the European Parliament (Cambridge: Cambridge University Press, 2006)Google Scholar.

⁶ Poole, and Rosenthal, , CongressGoogle Scholar.

⁷ However, see Snyder, James M. Jr, ‘Committee Power, Structure-Induced Equilibrium, and Roll Call Votes’, American Journal of Political Science, 36 (1992), 1–30CrossRefGoogle Scholar; Londregan, John, Legislative Institutions and Ideology in Chile (New York: Cambridge, 2000)CrossRefGoogle Scholar; and Cox, Gary W. and McCubbins, Mathew D., Setting the Agenda: Responsible Party Government in the U.S. House of Representatives (Cambridge: Cambridge University Press, 2005)CrossRefGoogle Scholar.

⁸ This argument forms the underpinning of studies finding that candidate selection affects behaviour of legislators and thus party cohesion (e.g., Michael Gallagher, ‘Introduction’, in Gallagher, Michael and Marsh, Michael, eds, Candidate Selection in a Comparative Perspective (London: Sage, 1988), pp. 1–19, p. 15)Google Scholar. Only if party leaders can observe in roll call votes the behaviour of their party colleagues may the former affect the behaviour of the latter.

⁹ See Interparliamentary Union, Parliaments of the World: A Reference Compendium (London: Macmillan, 1986)Google Scholar.

¹⁰ Saalfeld, Thomas, ‘On Dogs and Whips: Recorded Votes’, in Herbert Döring, ed., Parliaments and Majority Rule in Western Europe (New York: St Martin’s Press, 1995), pp. 528–565Google Scholar; Carey, John M., ‘Visible Votes: Recorded Voting and Legislative Accountability in Latin America’ unpublished paper, April 2004, and Interparliamentary Union, Parliaments of the World: A Reference Compendium (2004)Google Scholar.

¹¹ The detailed country-specific information appears in the Web Appendix published as Supplementary Material at www.journals.cambridge.org/jps. Given the rather eclectic set of sources, this table should only be considered as an illustration.

¹² The upper house refrained from introducing such a system and has only used roll call votes very infrequently, see von Wyss, Moritz, ‘Die Namenabstimmung im Ständerat: Untersuchung eines parlamentarischen Mythos’, in Isabelle Häner, ed., Nachdenken über den demokratischen Staat und seine Geschichte: Beiträge für Alfred Kölz (Zurich: Schulthess, 2003), pp. 23–47.Google Scholar

¹³ Since 1 December 2003, all votes recorded by the electronic voting system may be consulted, but only the categories mentioned above, plus a new category of votes on financial matters involving large sums, are published in the minutes of parliament.

¹⁴ The Swiss Parlamentsdienste made this dataset available to us, on condition that the confidentiality of the individual votes should be respected. Hence, I cannot make the data I used accessible and can only offer averages and other summaries of those data.

¹⁵ Obviously, biases are also to be expected in dimensional analysis of roll call votes, as the rather powerful analysis of the European parliament by Gabel, Matthew J. and Carrubba, Clifford J., ‘The European Parliament and Transnational Political Representation: Party Groups and Political Conflict’, Europäische Politik, 3 (2004), 1–9Google Scholar; and Carrubba, Clifford J., Gabel, Matthew, Murrah, Lacey, Clough, Ryan, Montgomery, Elizabeth and Schambach, Rebecca, ‘Off the Record: Unrecorded Legislative Votes, Selection Bias and Roll-Call Vote Analysis’, British Journal of Political Science, 36 (2006), 691–704, illustratesCrossRefGoogle Scholar.

¹⁶ For an overview over the Swiss party system, see Ladner, Andreas, ‘Das Schweizer Parteiensystem und seine Parteien’, in Ulrich Klöti, Peter Knoepfel, Hanspeter Kriesi, Wolf Linder and Yannis Papadopoulos, eds, Handbuch der Schweizer Politik (Zürich: Verlag Neue Zürcher Zeitung, 1999), pp. 213–260Google Scholar.

¹⁷ Rice, Stuart A., ‘The Behavior of Legislative Groups: A Method of Measurement’, Political Science Quarterly, 40 (1925), 60–72CrossRefGoogle Scholar.

¹⁸ In this last case, however, the very small number of votes used to determine the Rice index is probably the main explanation for the lack of difference.

¹⁹ It might also be the case that in the final passage votes the party whips are used more regularly to achieve a higher party discipline. I thank Gail McElroy for suggesting this interpretation.

²⁰ For the literature on ideal-point estimation attempts to use information on y to estimate X, see Poole, Keith, Spatial Models of Parliamentary Voting (New York: Cambridge University Press, 2005)CrossRefGoogle Scholar.

²¹ Heckman, James J., ‘The Common Structure of Statistical Models of Truncation, Sample Selection and Limited Dependent Variables and a Simple Estimator for Such Models’, Annals of Economic and Social Measurement, 5 (2005); 475–492Google Scholar.

²² E.g., Heckman, , ‘The Common Structure of Statistical Models of Truncation, Sample Selection and Limited Dependent Variables and a Simple Estimator for Such Models’Google Scholar; Maddala, G. S., Limited Dependent and Qualitative Variables in Econometrics (Cambridge: Cambridge University Press, 1983)CrossRefGoogle Scholar; Achen, Christopher H., Statistical Analysis of Quasi-Experiments (Berkeley: University of California Press, 1986)Google Scholar; Dubin, Jeffrey A. and Rivers, Douglas, ‘Selection Bias in Linear Regression, Logit and Probit Models’, in John Fox and Scott J. Long, eds, Modern Methods of Data Analysis (Newbury Park, Calif.: Sage, 1990), pp. 410–442Google Scholar; and Breen, Richard, Regression Models: Censored, Sample Selected or Truncated Data (Thousand Oaks, Calif.: Sage, 1996)CrossRefGoogle Scholar.

²³ To address possible selection biases in ideal-point estimation, the careful analysis of the possible endogeneity of roll calls by Clinton offers interesting avenues, see Clinton, Joshua D., ‘Testing Lawmaking Theories with (Endogenous) Roll Calls, 90th–106th U.S. House’ (unpublished paper, Department of Politics, Princeton University, 2006)Google Scholar.

²⁴ Rice, , ‘The Behavior of Legislative Groups’Google Scholar.

²⁵ Here I obviously gloss over the fact that I have not yet specified how one equation relates to another. Normally, this link would be provided by a probit or logit function, but in the following – for presentational purposes – a linear relationship is assumed.

²⁶ This works only, however, if the dependent variable Y in Equation 6 corresponds to the majority vote of each party group. This also requires the appropriate changes in the signs of the independent variables. In addition, this derivation suggests heteroscedasticity due to different sizes of party groups and a special variance-covariance matrix, which I address by estimating clustered standard errors.

²⁷ See Appendix Table 1A for the various categories coded in the dataset I used.

²⁸ Obviously, given the rather important differences in cohesion scores between automatically published votes and all others, this makes my task of correcting estimates of cohesion scores more difficult.

²⁹ Heckman, , ‘The Common Structure of Statistical Models of Truncation, Sample Selection and Limited Dependent Variables and a Simple Estimator for Such Models’Google Scholar.

³⁰ This procedure corresponds to the two-step estimator proposed by Heckman and discussed in detail by Achen ( Heckman, , ‘The Common Structure of Statistical Models of Truncation, Sample Selection and Limited Dependent Variables and a Simple Estimator for Such Models’Google Scholar; Achen, Statistical Analysis of Quasi-Experiments). I also estimated all models with a full-information maximum-likelihood model and obtained largely identical results.

³¹ I refrain from reporting the results of the linear regressions, since Table 4 indirectly reports the estimated coefficients.

³² Hug, Simon, ‘Selection Bias in Comparative Research: The Case of Incomplete Datasets’, Political Analysis, 11 (2003), 255–274CrossRefGoogle Scholar.

³³ Gabel, and Carrubba, , ‘The European Parliament and Transnational Political Representation: Party Groups and Political Conflict’Google Scholar, and Carrubba, et al. , ‘Off the Record’Google Scholar.

³⁴ Carrubba, Clifford J. and Gabel, Matthew, ‘Roll Call Votes and Party Discipline in the European Parliament: Reconsidering MEP Voting Behavior’ (paper prepared for presentation at the American Political Science Association Annual Meeting, Atlanta, 1999)Google Scholar.