Abstract
Using the first dimension of DW nominate scores for the U.S. House and Senate over the period 1956–2004, we analyze how the degree of ideological polarization between the parties varies as a function of district ideology, defined in terms of Democratic presidential support in the district. We find, as expected, that the more Democratic-leaning the district at the presidential level the more liberal are the representatives from the district, and that for any given level of Democratic presidential support, Democrats elected from such districts are, on average, considerably more liberal than Republicans elected from such districts. However, we also find that—consistent with theoretical expectations of spatial models that have recently been put forward—the ideological difference between the winners of the two parties is as great or greater in districts that, in presidential support terms, are the most competitive—a finding that contradicts the intuitive expectation that the pressure for policy convergence is greatest when the election is most competitive.
We are indebted to Keith Poole for making available to us Poole-Rosenthal DW-NOMINATE data for the House for the period of interest, and to Dan Butler for helpful comments on a previous version of the manuscript. We also owe special thanks to Clark Bensen of POLIDATA who routinely provides us with high quality aggregate election data. We are indebted to Clover Behrend-Gethard and Sue Ludeman for bibliographic assistance. The listing of authors is alphabetical. Work on this project by the third-named author was supported by SSHRCC research grant #410-2007-2153 (co-PIs Stanley Winer and J. Stephen Ferris) and by the Jack W. Peltason (Bren Foundation) Chair, University of California, Irvine.
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Notes
- 1.
- 2.
- 3.
- 4.
See Grofman (2004) for a recent review of the theoretical literature on party divergence in plurality elections.
- 5.
- 6.
Grofman et al. (1999) report analyses suggesting that the policy preferences of state-level Democratic partisan constituencies are substantially more heterogeneous than are the policy preferences of state-level Republican constituencies, and that this difference is not an artifact of the fact that Democratic partisans from the South hold substantially more conservative views than do Democrats from the rest of the country.
- 7.
In a study of postwar presidential elections, however, Kenny and Lotfinia (2005) report mixed results, i.e. they report that in some sets of analyses the presidential nominees who were closer to their party’s ideological position fared better in general elections, while other sets of analyses suggest that the nominees who were closer to the median voter appeared to be electorally advantaged.
- 8.
In particular, Griffin finds that the slope over districts relating average representative ideology to (normalized) presidential vote is steeper for competitive (moderate) districts than for lop-sided districts. He further finds that within districts legislators are more likely to adjust to changing voter ideology over time in competitive rather than uncompetitive districts.
- 9.
Our evidence does not speak to a current lively debate over issue ownership and dialogue in political campaigns, which revolves around whether rival candidates emphasize the same policy issue areas, not whether the candidates take similar positions on these issues (see, e.g., Sigelman and Buell 2004; Petrocik 1996; Kaplan et al. 2006).
- 10.
Using district-level estimates of the voter distribution, Butler (2009) explains polarization among candidates in terms of the location and size of candidates’ bases and proportion of swing voters.
- 11.
In competitive House elections, even if the positions of the House candidates do not greatly affect actual turnout, they may affect the decision to vote in the House contest and will likely affect the efforts of potential activists (cf. Schofield and Miller 2007).
- 12.
More generally, using a conditional logit model, Adams et al. (2010) argue that the more uncommitted a voter’s decision to vote for a candidate, the more the candidate will take the voter’s preferences into account (Erikson and Romero 1990, p. 1107). In a two-candidate election where voters have nonzero probabilities of abstaining, the higher of the voter’s probabilities of voting for one or the other of the candidates must be the one nearer 0.5, and hence the voter is most marginal with respect to the candidate that she is most likely to support. Given that partisan voters are more likely to vote for their party’s candidate than for the opposition party’s candidate, candidates attach greater weight to the policy preferences of the members of their own partisan constituency than to the preferences of the members of the rival candidate’s constituency.
- 13.
See, Schofield and Sened (2006).
- 14.
- 15.
See Callander and Wilkie (2007).
- 16.
In fact for an extreme case in which vote-share is completely determined by spatial factors—namely the candidates’ relative proximities to the median voter—the slope for each party would be decidedly positive rather than negative, i.e., more liberal Democratic candidate positioning would be associated with lower Democratic vote shares (and vice versa for Republicans). To see why regressing against vote shares in House districts biases toward positive slopes, consider a scenario in which the voters are uniformly distributed on the interval from –0.5 to 0.5 (the center half of the Left-Right scale from—restricted and, on average, less liberal). This leads to a positive slope when spatial position is regressed against Democratic vote-share. So endogeneity can seriously bias inferences from data that relate spatial position to Democratic vote-share in district House races. Regressions of DW-NOMINATE scores against House vote-shares that we have done give lines that are essentially flat. We take this as evidence of significant endogeneity effects (data omitted for space reasons).
- 17.
As explained in the website http://polisci.ucsd.edu/faculty/poole.htm, the average DW-NOMINATE coordinate for every legislator is constrained to lie within the unit hypersphere, with +1 interpretable as the most conservative score and −1 interpreted as the most liberal score. However, some members may have large linear terms so that for some Congresses their coordinates can be greater than +1/–1. In our data, there are 12 data points for which the DW-NOMINATE scores are beyond the range of −1 or 1.
- 18.
Specifically, the normalized Democratic vote proportion for president is equal to district presidential vote share minus the national presidential vote share. For example, if a presidential candidate gets 65 percent in a district, and 60 percent nationally, then the normalized district percent is 65−60=+5 percent, reflecting the fact that the presidential candidate ran five percentage points ahead of his national average in that district. If the presidential vote share in the district is the same as the national vote, then the normalized district vote is zero percent. Centering the district vote on zero is necessary, as explained in footnote 20 below, in order for the quadratic regressions (described below) to generate informative parameter estimates. Because the mean of the national Democratic presidential vote over the period of the study (49.9 %) is almost exactly 50 percent, we may interpret the zero point of the normalized Democratic vote proportion for president as representing either the mean national presidential vote or as zero deviation from a 50–50 district.
- 19.
We define the south as Arkansas, Alabama, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, Texas, and Virginia.
- 20.
To see why it is necessary to employ a measure of district ideology that is centered on zero in order to estimate informative parameters in (1), note that in a quadratic regression, parameter estimates reflect behavior around the zero point of the independent variable. If we use the actual district vote as our measure of district ideology, then the zero point of this independent variable corresponds to a district where the Democratic candidate received zero percent of the presidential vote, which is outside the range of interest. Under this parameterization, estimates would reflect behavior over an unrealistic region. Using the normalized Democratic vote proportion for president, on the other hand, places the zero value of the independent variable at a district whose presidential vote matches the national presidential vote, focusing attention on behavior around competitive electorates.
- 21.
For simplicity, the party-specific regression curves and their confidence intervals in the figures are based on the full data set without the breakdown by region.
- 22.
These estimates apply to marginal changes in district presidential vote when the Democratic vote share in the district is similar to the national vote (so that the normalized measure of district ideology is near zero), in which case the value of the squared district ideology variable in (1) is negligible. In this range of values the predicted effect of district ideology on representatives’ DW-NOMINATE scores is approximately linear.
- 23.
The partisan gaps reported above apply to the reference category, non-South. For the category South, the estimated intercept and parameter estimate for the variable South must be combined, so that the partisan gap in the South ranges from 0.32–0.33 in the first two subperiods to 0.69 in the most recent subperiod.
- 24.
We note that Ono (2005) obtains similar plots for two Congresses (1969–1970 and 2003–2004) and observes the increasing polarization of the parties in Congress. Similarly, Clinton (2006), using samples that aggregate to over 100,000 voters, finds systematic differences in Republican and Democratic voting behavior in the 106th House (1999–2000) that cannot be entirely accounted for by same-party constituency preferences.
- 25.
Figure 4 in Butler (2009) appears to suggest this same convexity for Democrats and concavity for Republicans.
- 26.
One explanation for convex curvature of the Democratic scores in the earlier part of the period under study may be that a number of conservative Southern Democrats won uncontested races, causing the quadratic regression curves for Democrats to turn up on the right side of the scale. But controlling for districts in the South as we have done should reduce this effect and, in any event, it cannot explain the pronounced convex curvature for the Democrats in the most recent subperiod.
- 27.
Erikson and Wright (2000, Fig. 8.1) also plot roll-call ideology based on the ADA/ACA indices for the 1980s against presidential vote, obtaining similar patterns; linear regression results are reported for the period 1976–1996. The authors note that “Districts in the middle are generally represented by relatively moderate Republicans or relatively moderate Democrats,” but these authors do not assess the size of the ideologically gap between Republicans and Democrats as a function of district ideology. The fact that representatives from competitive districts tend to be more moderate than those from lopsided districts does not imply that the partisan gap between the sets of Republican and Democratic winners in moderate districts is smaller than the corresponding gap for more extreme districts.
- 28.
As with our analyses of House districts (see footnote 18), for the Senate-based analyses our measure of ideology was the difference between the state’s Democratic presidential vote and the national Democratic presidential vote, a measure that is centered on zero.
- 29.
Restriction of the data to open-seat races changes the pattern only very marginally, with a slight tendency for Republicans to be more moderate in competitive districts. Furthermore, the patterns observed are not likely the result of the particular measure (DW-NOMINATE scores) of ideological voting in the House that we have used. Lee et al. (2004) plot legislative voting records as assessed by NOMINATE scores and by each of fifteen monitoring associations ranging from the liberal American for Democratic Action (ADA) to the conservative League of Conservative Voters (LCV) (against the Democratic vote share in the House election by district). These plots show internal consistency among many different measures of ideological voting in Congress.
- 30.
Bishin et al. find that this conclusion holds regardless of whether the state electorate’s diversity was measured in terms of demographic characteristics (using the Sullivan index) or in terms of ideological diversity.
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Adams, J., Brunell, T.L., Grofman, B., Merrill, S. (2013). Do Competitive Districts Necessarily Produce Centrist Politicians?. In: Schofield, N., Caballero, G., Kselman, D. (eds) Advances in Political Economy. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-35239-3_16
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