The Limited Explanatory Power of the Median Voter Theorem

Tyler Cowen thinks people should talk more about the median voter theorem when trying to understand what’s happening in politics. I disagree. I mean, admitted the phrase “median voter theorem” is almost never used in newspapers, but I think the conventional political media wisdom tends to drastically overstate voter preferences as an explanatory variable. Andrew Gelman also has his doubts about the importance of the median voter theorem, citing data which indicates that a moderate voting record only modestly boosts your ability to win elections:

The United States Senate also provides a convenient test of this idea, since it offers up a series of pairs of politicians who are accountable to identical groups of voters. But when you look at opposite-party senate pairs, you don’t see a great deal of similarity in their voting records. Or to look at it another way, everyone knows that the voters in Louisiana are more liberal than the voters in Iowa. And this helps explain why Mary Landrieu is more conservative than Tom Harkin. But Mary Landrieu isn’t more conservative than Chuck Grassley. The ordering of those states’ four Senators, from left to right, is Harkin (D-IA) then Landrieu (D-LA) then Grassley (R-IA) then Vitter (R-LA) — the partisan affiliation of the senator tells you more about their voting behavior than does knowledge about the electorate they represent. Indeed, in terms of DW-NOMINATE exactly zero Senate Democrats in the 110th or 109th Senates compiled a voting record more conservative than that of the leftmost Republican (first Chaffee then Olympia Snowe) even though in both cases many Democrats represented states whose median voters are more conservative than the median voter in Maine or Rhode Island.

Part of the answer here is presumably that it’s relatively rare for an incumbent American politician to actually face a competitive re-election bid. Incumbent Senators do frequently form cross-party alliances to defend parochial local interests, for fairly obvious reasons, so it’s not as if people are behaving recklessly with their careers. Helping out local influentials is presumably not only (locally) popular, but actually helps ward off challengers. I would also note that it’s not obvious to me how an incumbent politicians would really go about assessing median voter sentiment—issue polling is legendarily unreliable and subject to massive framing bias.