Do Moderate Voters Weigh Candidates’ Ideologies? Voters’ Decision Rules in the 2010 Congressional Elections

We note that the proposition that voters' issue intensity correlates with their position is consistent with the directional model of issue voting (Macdonald et al. 2007; Rabinowitz and Macdonald 1989), which posits that citizens who self-place at the center of the policy/ideology scale are “neutral” and thus do not decide based on the parties'/candidates' positions on the focal issue. Warwick (2004) has argued that this intensity component of the model should be tested separately from the directional component. This is what we do here although our purpose is not to test the directional model, nor is it to assess the relative merits of the directional versus proximity models. As noted by Lewis and King (1999), it is difficult to parse out these competing models using election survey data.

Ansolabehere et al. (2008) show that this approach significantly reduces measurement error in characterizing respondents' preferences.

We estimated 50,000 iterations after a burnin period of 10,000, and thinned by 100 to generate a posterior distribution of respondent ideology with sample size 500.

The 2010 phase of the study was based on the same districts sampled in the 2006 study. For more information about the study, see the project website: [Identifying reference removed]. Below we report results on all 155 districts, although our results replicate when we restrict the analysis to the random sample.

Because the study surveyed experts in both political parties, we correct for partisan bias in individual expert informants' candidate placements. Individual informants' ratings were corrected for partisan bias by regressing the candidate rating on the partisanship of the informant relative to the candidate (“same party” = 1; “independent” = 0; “opposite party” = −1), and then subtracting the resulting coefficient on partisanship from the individual informant's rating of the candidate. We note that we also estimated models where we did not correct for experts' partisan bias, and these estimates supported the same substantive conclusions we report below. This is not surprising given that Maestas et al. (2014) demonstrate that correcting for partisan bias has only a small effect on estimates based on informant samples of the size used in this study.

In assuming that the positions of mass and district-expert responses on the liberal-conservative scale are equivalent, we follow a long line of scholarship comparing the positions of activists and others with those of ordinary voters (Kirkpatrick 1975; McClosky et al. 1960; Miller and Jennings 1987).

Elsewhere we have reported analyses supporting the reliability and validity of our district-expert candidate ideological placements [author cites].

This relationship is not due simply to partisan polarization: the correlation between the informant placements and a composite DW-NOMINATE/ADA ratings among Democratic incumbents is 0.70; among Republicans it is 0.56.

For examples of research that uses Project Vote Smart to characterize candidate ideology, see Ansolabehere et al. (2001), Rogowski (2014), and Shor and McCarty (2011).

In 2010, about a quarter (196) of major-party House candidates completed the survey. We used two supplementary sources of information for those candidates who did not complete the survey. First, Project Vote Smart researched issue positions for candidates who did not complete the survey, and displayed these positions (along with their research sources) on their website (http://​www.​votesmart.​org/​voteeasy). Second, under the assumption that political elites are ideologically consistent across time, we also used a candidate's prior responses to the Vote Smart surveys. For instance, if a candidate completed the survey in 2008, we also used those responses to generate our estimates.

We emphasize, however, that while these 15 questions allowed us to create a common space for candidates and voters, we used available data on candidates' and voters' policy positions to generate the estimates. Thus, our estimates have a high degree of precision, particularly in comparison with other research that uses relatively few roll call voters or implied policy positions to jointly scale voters and politicians (e.g., Bafumi and Herron 2010; Jessee 2010).

The standard deviation for Democratic and Republican candidates was 0.56 and 0.34, respectively. The locations for Democrats ranged from 1.38 to 4.30, and Republican locations from 4.88 to 6.72.

The standard deviation for Democratic and Republican candidates was 0.48 and 0.40, respectively. The locations for Democrats ranged from −2.04 to 1.28, Republican locations from −0.41 to 1.90.

Sophistication is measured using a battery of eight political knowledge questions relating to the party in control of state and federal institutions (U.S. Senate, U.S. House of Representatives, state senate, and state lower house) and name recognition of state and federal representatives (U.S. Senators, governor, and U.S. House Representative). Respondents who answered all eight questions correctly are classified as politically sophisticated.

Strong partisans were defined as those who placed themselves at the extremes of the one to seven party identification scale (1 or 7).

Respondents who were unwilling to assess the ideology of both candidates using the one to seven ideological scale were categorized as placing neither candidate. Respondents were considered to have placed both candidates correctly if they placed the Republican candidate to the ideological right of the Democratic candidate.

Analyses based on a quadratic loss function [(v _ij  − D _j )² − (v _ij  − R _j )²] support the same substantive conclusions that we report below.

We note that we also re-estimated our models while including separate dummy variables for Democratic and Republican incumbents, and these analyses supported the same substantive conclusions that we report below.

We note that the 288 House races for which we have measures of operational ideology do not perfectly overlap with the 155 House races for which we have measures of symbolic ideology. However, we obtain results substantively identical to those shown in Tables 1, 2 and 3 when using our measure of operational ideology for just those races for which both measures were available. These results are shown in Table A-2 in the supplementary appendix.

This effect is calculated for an independent voter residing in an open-seat district, where the Democratic and Republican candidates spend equally, and all other variables in the model are set to their mean or modal values, as appropriate.

As summarized by Grofman (2004), this includes a focus on redistricting; primary elections; politicians' policy objectives; candidates' desire to deter entry by extreme protest candidates; incumbents' desires to achieve party leadership positions; candidates' needs to motivate turnout among their core supporters; and, the desire to generate campaign contributions from interest groups with noncentrist policy views.