Left-right ideology of voters, congressmembers, and senators

These plots from John Sides reminded me of some graphs from our forthcoming Red State, Blue State book that display the distributions of voters, House members, and senators on a common scale:


House members and senators’ positions are estimated based on their votes in Congress.  Voters’ positions are estimated based on some survey questions where people were asked their views on a number of issues that had also been voted on in Congress.  As you can see, elected representatives are generally more extreme than voters.

Polarization in red, purple, and blue states

We also looked at these distributions among Republican, battleground, and Democratic states (categorized based on their presidential voting patterns in 2000 and 2004). Geographic polarization is strong, especially in the Senate:


Voters in Republican and Democratic states are slightly more conservative and liberal, respectively, on the issues. Elected representatives are more geographically polarized: winner-take-all elections generally magnify differences that are already there. In a strongly Democratic-leaning state, it is likely that both senators will be Democrats and will be on the left side of the political spectrum. Such a state will also typically have many strongly Democratic congressional districts. The reverse pattern holds in Republican states.

More detail is in chapter 8 of the book, and lots of other information is in an article by Joe Bafumi and Michael Herron.

9 thoughts on “Left-right ideology of voters, congressmembers, and senators

  1. These observations are interesting, but I am not sure what we can learn from them. I see some problems with comparing highly scrutinized and carefully thought out views of full-time politicians and on-the-fly views of private citizens. Also, the electorates in “battleground states” and “Democratic states” appear very similarly distributed, but they elect vastly different politicians. How would you explain that? Is something mismeasured here?

  2. You haven’t really shown anything here. Even if your sample size is adequate (which is impossible to say, since you gave no data on it), all that we know from this data is that (possibly correlated, or possibly not) bimodal distributions are similar to each other. That is vague and meaningless. A chihuahua and a doberman are both dogs (and hence similar).

  3. Bullfighter:

    I agree with your first point (as noted in my subsequent blog entry). On your second point: it doesn’t take a big shift in votes to move the balance of power from one side of 50% to the other.


    You can read the Bafumi and Herron paper for more detail. Here’s a version of their paper from last year that discusses sample size etc.

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