Wendy Tam Cho on Voter Migration and Partisanship

This week UIUC professor Wendy Tam Cho shared ongoing research on patterns of voter migration and partisanship (joint work with James Gimpel and Iris Hui). Cho and co-authors have compiled state level voter files from a selection of states and use the data to track voters as they move within and across state boundaries.

Cho frames this work as an empirical evaluation of Bill Bishop’s book, The Big Sort (at Amazon). Bishop’s position is that people are self-sorting into homogeneous neighborhoods and social networks. Whereas people formerly found themselves in diverse neighborhoods or social groups, modern housing patterns and a lack of cross cutting networks diminishes the opportunities for citizens to encounter different viewpoints and political positions. As a result, the nation is polarizing.

By matching voters across several years of voter file, Cho and co-authors can track voters as they move within a state or across a limited number of state lines (provided they re-register at the new address). Voter files do not usually contain very much information (often not much more than name, address, and age — only what is necessary to establish residence and minimum age for voting), but in some cases, states provide an opportunity to register with a party either during registration or when voting in a primary (rules vary as to when and how one registers, a point to which I will return later). In addition to tracking changes in address, Cho and co-authors track changes in party registration as voters move. They also aggregate party registration to get a sense of the districts in which voters live.

Combining this data, they find that much of voter migration is driven by improving life circumstances. Measurements such as income in the new district, miles of parks, and other measures of quality of life are linked with most voter migration. They also find that almost everyone is moving to more Republican districts, both voters registered as Republicans and voters registered as Democrats. In part, these two findings may be identical in a sense. If movements indicate increasing wealth, we may well expect movements into more Republican strongholds by all movers. Perhaps more interesting is focusing in on people who switch party registration after moving. The authors find that voters switching from Republican to Democrat registration are more likely to move to a more Democratic area. On balance, this is mixed evidence for Bishop’s position. While some people are moving to more homogeneous areas, others are not.

While I think this is interesting work, I have some concerns about the use of party registration as a measure for political ideology, party attachment, or vote choice. In fact, I am not exactly sure what party registration indicates. Party registration has different implications in different states. For example, California allows voters to register with a party, but independents may vote in any party’s primary election (semi-closed primaries). Neighboring Nevada, however, has fully closed primaries that allow only party members to vote in party contests (independents may still vote in non-partisan contests). On face, the nature of party registration in these two states is very different. In Nevada, if an independent wishes to participate in a major party’s primary, he or she must re-register in advance as a party member. In California, the same voter would only have to show up on election day and select the appropriate ballot. Other states allow re-registration for party on the day of a primary, which could potentially lead to a large amount of switching, depending on the hot races in a given election year. Still other states have completely open primaries where voters can pick any party ballot without re-registering, minimizing the need to switch party registrations at any time (some of these states do not even have party registration at the state level, which I would argue is more than a mere measurement problem for this research). These different institutional rules change the importance and meaning of party registration from state to state.

Could these variations systematically bias the data Cho and co-authors share? Quite possibly. Participation in the 2008 Democratic presidential primary exceeded previous contests by a wide margin. In some cases, the participants were new to primary politics, but at some of them re-registered. Rush Limbaugh encouraged his listeners to vote in the Democratic primary (and throw their support to the second place candidate) to prolong the uncertainty of the Democratic candidate in November. Depending the state, a Limbaugh fan or a newly interested independent could have either re-registered or just picked up a ballot on election day. In one case, the voter shows up as a switcher and in the other case does not. Generally, if a voter simultaneously moved and registered Democratic in 2008, what does that really tell us about this person’s partisanship? I’m not sure. Such bias may work against Cho and co-authors, making their results more surprising, but I consider it a problem in either case.

I do not think party registration is an informationless measure, but I challenge Cho and co-authors to provide more information on exactly what party registration indicates. Does it correlate with other measures of ideology and partisanship? Does it predict vote choice? Are there other variables that moderate these relationships? For example, how do differences in registration laws moderate the link between party registration and vote choice? These questions are largely empirical, and I think would provide useful information to evaluate these interesting findings more carefully.