Another Look at Party Discipline

Steve Smith sends this graph:

In the political science literature, DW-NOMINATE scores a the most prominent measure of the ideology of members of Congress.  This graph plots the standard deviation in those scores from the 84th through 111th Congresses (basically 1955-2010).  The larger the standard deviation, the more ideological heterogeneity there is in the party.

In the earlier part of this period, the Democrats were clearly more heterogeneous, as one might expect in a party with defined liberal Northern and conservative Southern wings.  But over this period, ideological heterogeneity in the Democratic Party decreases substantially.  By about the 104th Congress (after the “Republican Revolution” of 1994), the parties are equally heterogeneous.   And that has continued to be true.  Via email, Smith says:

There is hardly any difference since start of the Gingrich era (he became Republican whip in 1989).  ”Gingrichism” encouraged a disciplined party to sharpen differences (he thought the public was on his side) and force Democrats to cast more difficult votes (he thought this would put Democrats from conservative districts in danger).  Republicans gave this strategy credit for the 1994 victory.  For detail, see Barbara Sinclair’s Party Wars.

Democrats’ reputation for less discipline, or at least less cohesiveness, was certainly deserved in the period between the late 1930s and 1980s.

Of course, DW-NOMINATE scores are based on roll call votes, as are party unity scores.  But political scientists still interpret these trends as reflecting genuine changes in the ideological composition of the party, not simply as evidence that the parties are smarter about which bills they bring to the floor.  Indeed, it’s hard to imagine that the conversion of conservative Southern Democrats to Republicans, or their replacement by Republicans, wouldn’t have genuine ideological implications.  For these same reasons, party unity scores are relevant to the question of party discipline as well.

In sum, both parties, and especially the Democratic Party, have become more ideologically homogeneous and also more polarized.  As a consequence, congressional representatives of both parties are more willing to empower leaders, precisely because members can be confident that leaders will follow what the party rank-and-file want.  (This is conditional party government theory.)  As a consequence, there is also growing unity in party behavior on the floor.

Most importantly, these data provide another piece of evidence counter to Westen’s notion that Democrats are fundamentally less cohesive or disciplined than Republicans.  See also my two previous posts.

4 Responses to Another Look at Party Discipline

  1. Andrew Gelman November 1, 2011 at 9:17 pm #


    To repeat what I wrote earlier:

    You gives some reasons why viewers of the political scene might think that congressional Republicans are more disciplined than their Democratic counterparts, even if this isn’t really so.

    I’d like to give one more big reason based on recent history. When Barack Obama became president, congressional Republicans implemented a solid No strategy and were successful at stopping much of the Democrats’ agenda. With only 40% of each of the houses of Congress, the Republicans had few tools except party discipline. To me, it is this impressive achievement that earns congressional Republicans their reputation.

    Everything you wrote is fine but I think you’re missing the elephant in the room (so to speak).

    • John Sides November 1, 2011 at 9:27 pm #

      Andy: You do like that pun. I agree that the GOP strategy after 2009 is a possible source for some contemporary repetitions of this stereotype. But it strikes me that the stereotype goes back much further than this.

  2. Jon November 2, 2011 at 1:35 am #

    Alternatively, Republicans *could* be more “disciplined” if they represent more homogenous constituencies than Democrats. A cursory look at this relationship using the Levendusky and Pope heterogeneity data indicates that Republican members of the Senate *do* represent more ideologically homogenous states.

  3. Peter November 2, 2011 at 12:19 pm #

    I think the other thing worth considering here is the distribution of voters in congressional districts. Many observers (Jacobson, etc.) have pointed out that a majority of congressional districts favor Republicans because their voters are more efficiently distributed than Democrats. The consequence is that Democrats must win congressional districts that vote for Republican presidential candidates in order to control the House and successful candidates tend to be moderate (e.g. Heath Shuler in North Carolina or Stephanie Herseth-Sandlin in South Dakota). See Karen Price’s documentary “Housequake” for a great illustration of Rahm Emmanuel recruiting moderates to take the House in 2006. I think that’s one reason why you see the ideological diversity of House Democrats spike in Steve’s graph above when we hit the 110th Congress. So even while both parties have become more homogenous overall, my expectation for the comparative ideological diversity of the two parties is that the diversity of Democrats will go up more when they are in the majority than will be true of Republicans.