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Cox, Kousser, and McCubbins: What polarizes parties

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State Politics

Cox, Kousser, and McCubbins. 2005. What polarizes parties? Preference and agenda control in American state legislatures. APSA paper.


Similar to Kim (2005), the authors look to state politics to put the cartel theory (Cox and McCubbins 1993) and the preferences theory (Krehbiel 1993, Mayhew 1974) head to head. The cartel theory wins: By using agenda control (X), parties influence outcomes (Y).


Rolled: The majority gets rolled if a majority of the majority did not support a bill that passed. (A minority gets rolled if a majority of the minority did not support a bill that passed).


If only preferences mattered (i.e. if there were no agenda control), then you would expect to see the majority get rolled as frequently as the minority (given their different proportions in the legislature, of course). With agenda control, however, majority party leaders prevent majority rolls by keeping bills that might lead to a roll off the agenda. Thus, agenda control creates the illusion of increased legislative polarization (because the moderates don't get a chance to defect--the only bills that come up for a vote or the ones that moderates don't want to defect on).

Specific predictions deal with (1) how often the majority is rolled, (2) how often the minority is rolled, (3) what proportion of passed bills move policy left/right, and (4) legislative polarization.


See table 2. Although rolls are rare in both treatment and control groups, majority rolls are apparently more frequent without agenda control. (In my view, the results are very weak, however).

Table 3 presents stronger evidence in support of th authors. In addition, the Republican majority in Colorado allowed far more leftward-moving bills to pass without agenda control than with agenda control. Similarly, the Democratic majority in California allowed far more rightward-moving bills to pass without agenda control than with.

Also, a comparison of Figures 6 and 7 shows that partisan polarization is much more evident when there is agenda control (in California).