Party ID in States Shifted in 2006

Democrats gained an average of 3.4% and Republicans lost 3.0% in partisan identification between 2005 and 2006, according to a new Gallup estimate based on over 30,000 interviews conducted throughout 2006. Gallup aggregated polls throughout the year to create estimates of party identification at the state level, as they did in 2005 and previous years. Gallup's report of the results is here.

The plot above shows how uniform the shift in Democratic and Republican partisanship was across the states. The colors of the points reflect the Democratic minus Republican balance in 2005-- the darker the blue the more net-Democratic identifiers and the darker the red the more net-Republican identifiers. Light or pale points are closely balanced states, as of 2005. The size of the points is proportional to the size of the state.

There is no apparent pattern to the shifts in partisanship: regardless of partisanship or partisan balance in 2005, states shifted by about the same amount in 2006. Likewise, Republican losses shifted uniformly. The +3.4 percentage point shift for the Democrats, and the -3.0 point shift against the Republicans produced a net -6.4 point loss for the Republicans in the balance of partisanship. The lower left figure in the plot shows that independents shifted more or less randomly between 2005 and 2006.

These shifts could, in principle, represent a non-trivial gain for the Democratic party. Recall that after the 2004 election there was considerable talk in Republican circles of establishing an "enduring Republican majority", a goal that seemed within the party's grasp though certainly not assured. That hope is clearly out of reach at the moment.

Before Democrats go wild with joy, there remains a question about the electoral impact of these partisan shifts. Party identification is the strongest single predictor of vote choice at the individual level. But the shifts in partisanship in the Gallup data do not predict the shift in voting for the U.S. House in 2006.

The bottom right figure above shows that the Republican U.S. House vote shifted more or less uniformly across states as well. However, when we look at the relationship between party id shift and vote shift across states, there is no relationship at all, as seen in the figure below.























Controlling for both Democratic gains and Republican losses doesn't add to the relationship. So the conclusion here is that both partisanship and vote shifted against the Republican party in 2006, but the variation in shifts appears to have been essentially independent between partisanship and vote.

Democratic gains and Republican losses in partisanship may affect the 2008 prospects in the House (and other) elections. But in 2006, it appears both vote and partisanship responded to conditions in the country without a clear impact of changes in partisanship on changes in vote.

Ideology and Republican Losses

Republican losses fell along most of the ideological spectrum, but were a bit more common among moderates than among the more conservative members of the party. The graph above shows the distribution of conservatism in the House of Representatives by party, using the National Journal ratings. (I use National Journal because it is convenient to grab the data, includes more votes than the typical interest group rating and correlates highly with other (more "political science-y") measures such as Nominate scores. Nominate scores are not yet available for the 109th Congress and I don't have time to compute them myself right now. Readers interested in how Nominate scores are computed should see Keith Poole's excellent site here.)

Republican incumbents who were defeated for reelection had an average conservatism score of 66.5, while those who won averaged 74.3, a statistically significant difference. (The average for all Republicans in 2005 was 73.2, and the median was 74.4.)

This does not mean that Republicans were necessarily more vulnerable BECAUSE they were more moderate. What is left out here is the district. Moderate Republicans are more likely to come from less conservative districts, so this result may well simply reflect the more competitive nature of districts that produce more moderate Republican members. I'll take a look at that later, but for now the simple point is that the election defeat did fall more heavily among representatives with somewhat more moderate voting records.

The one Democratic defeat plotted here is Rep. Cynthia McKinney, GA-04 who lost in the primary. The plot above also includes Republican Rep. Joe Schwartz, MI-07, who also lost in a primary.