why do legislators vote the way they do?

regression discontinuity

In this excellent paper, several professors try and look at what influences how a given legislator votes.

One view is that voters affect the voting records of legislators by inducing moderation. The idea is that the same democrat will vote more liberally if his district’s electorate is 60/40 in his favor rather than a 50/50 even split with republicans. In other words, voters help influence what policies a given legislators will support. The more secure he is, the more he will vote his personal preferences.

Another view is that voters only choose policies that are on offer, and have no effect on what policies are put before them. On this view, a democrat will always advocate his same chosen policies regardless of the composition of the electorate. He’ll vote the same way whether his district is 60/40 in his favor or 50/50 even.

Of course, in a given legislator, both effects are at work, but how to distinguish them. In this paper, a regression discontinuity approach is used to try and approximate a random assignment of partisan status to a district. This is accomplished by looking only at close elections.

The idea is this: take all the races that were decided in 1992 by less than 2% of the vote. Since it is essentially random who wins a race this close, like districts are essentially randomly assigned to be republican or democrat. Then, the difference in ADA vote score of those who are elected in 1994  (a measure of how liberal or conservative a legislator’s vote record on a scale of 100 is) is the average incumbency effect of party status. In other words, the difference between the ADA scores of legislators elected in 1994 who came from districts narrowly won by democrats in 1992 versus those who come from districts narrowly won by the republicans gives an estimate of the incumbency effect: how much easier it is to win an election when your party won the year before.

This total incumbency effect can then be decomposed into the two effects discussed above. Legislators running in a district that elected a democrat in the previous election will be more liberal than legislators running in a district that went republican the last time around for two reasons. 1) they will usually be democratic (the choose component above) and 2) incumbent democrats, now secure more in the electoral chances, will move to the left and vote more liberally.

Anyway, the punch line is that it seems that the choose effect dominates.

We find that voters merely elect policies: the degree of electoral strength has no effect on a legislator’s voting behavior. For example, a large exogenous increase in electoral strength for the Democratic party in a district does not result in shifting both parties’ nominees to the left. Politicians’ inability to credibly commit to a compromise appears to dominate any competition-induced convergence in policy.

This is because the electorate sees right through moderation and there is no way to guarantee commitment. If McCain promised liberal policies all over the board, he would not have been a rival to Barack Obama in 2008 because people know that he’s a republican and that he would just implement his desired republican policies upon election. Because candidates cannot credibly commit to moderation, voters have almost no effect on what policies candidates will vote for once elected. However, voters can effect, through the choice component, which set of policies are put into office.

In other words, voters don’t have much control over the bundles of policies they are faced with — they do not induce moderation. Instead, their power lies solely in picking which bundle of policies they will put in office.


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