In this post we continue our efforts to project partisan polarization in the next, 113th Congress. We previously did so for the 113th Senate; in this post we do so for the 113th House. To allow for cross-comparability with the Senate, we use members’ first dimension Common Space DW-NOMINATE scores, which measure their position on the liberal-conservative scale. Since there will be a large number of new members in the 113th House (79, 72 of which have never previously served in Congress), we must impute their DW-NOMINATE scores. We do so in the same manner as with the Senate: by regressing returning members’ DW-NOMINATE scores on personal and district characteristics, and plugging in those results for new members to predict their scores. Specifically, we use three variables to model ideological position: the partisan composition of the district (the PVI), whether they are female, and whether they are from a Southern state (the 11 states of the Confederacy, plus Oklahoma and Kentucky).
Below we show the results from two separate regressions (one for Democrats, the second for Republicans). The most important predictor of ideological position is the partisanship composition of the district. As expected, among Democrats, the bluer the district, the more liberal the Representatives; and vice versa for Republicans. The average effect of PVI is about the same for Democrats (b = 0.007) and Republicans (b = 0.009), but there is greater variability among Republicans (se = 0.002). Female Democratic Representatives are slightly more liberal (b = -0.03, p < 0.05), and Democrats from Southern states are slightly more conservative (b = 0.03, p < 0.15). Neither gender nor region are significant predictors of Republicans' Common Space DW-NOMINATE scores.
DEMOCRATS:
. regress dwnom pvi female south
Source | SS df MS Number of obs = 156
-------------+------------------------------ F( 3, 152) = 45.48
Model | 1.09152846 3 .363842819 Prob > F = 0.0000
Residual | 1.2161023 152 .008000673 R-squared = 0.4730
-------------+------------------------------ Adj R-squared = 0.4626
Total | 2.30763076 155 .01488794 Root MSE = .08945
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dwnom | Coef. Std. Err. t P>|t| [95% Conf. Interval]
-------------+----------------------------------------------------------------
pvi | .0074981 .0006825 10.99 0.000 .0061497 .0088466
female | -.032974 .016122 -2.05 0.043 -.064826 -.0011219
south | .0266996 .0177849 1.50 0.135 -.0084378 .0618371
_cons | -.3291223 .0127848 -25.74 0.000 -.3543812 -.3038634
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REPUBLICANS:
. regress dwnom pvi female south
Source | SS df MS Number of obs = 200
-------------+------------------------------ F( 3, 196) = 12.13
Model | .767726185 3 .255908728 Prob > F = 0.0000
Residual | 4.13637341 196 .021103946 R-squared = 0.1565
-------------+------------------------------ Adj R-squared = 0.1436
Total | 4.90409959 199 .024643717 Root MSE = .14527
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dwnom | Coef. Std. Err. t P>|t| [95% Conf. Interval]
-------------+----------------------------------------------------------------
pvi | .0092392 .0017622 5.24 0.000 .0057639 .0127145
female | -.0374514 .0378747 -0.99 0.324 -.1121456 .0372428
south | .0010773 .0233643 0.05 0.963 -.0450004 .0471551
_cons | .3880039 .0196807 19.71 0.000 .3491909 .426817
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Below we plot the distribution of first dimension Common Space DW-NOMINATE scores of members of the 112th House (in the top plot) and the 113th House (in the bottom plot). Our findings indicate that the 113th House will be about as polarized as the 112th House. The polarization measure (the difference in the mean scores of Republican and Democratic members) is 0.909 in the 112th House, and predicted to be 0.911 in the 113th House. The House will also remain the more polarized (though not by much) of the two chambers in Congress. These results concur with the popular account that: “If you didn’t like the 112th Congress, you will hate the 113th.”
Click image to enlarge
Note: We omit members of the seven undecided House races: AZ-2, AZ-9, CA-7, CA-52, FL-18, LA-3, and NC-7.