Self-reported legislator ideology versus interest group ratings

Legislative scholars are regularly concerned with the ideologies of the legislators they study. Although there are a host of possible ways to assess legislators' ideologies, the two most popular methods are the ratings by interest groups of the legislators' voting behavior, and the legislators' own self-reports of their ideology in mailed surveys. How do these measures compare with each other? In this article I compare the self-reports of ideology, as gathered in a survey of legislators in Connecticut, New York, and Vermont, with an index of their ideology based on a composite of various interest groups' rankings of their voting behavior during the same time period. By virtue of a tracking system, the identities of the individual survey respondents are known to me, thus allowing for linkage at the individual level of the self-reports to the interest group rankings. I find that the match between the two measures is strong, with some important caveats. In addition, the nature of the difference between the two measures yields an insight into the legislative politics of the three chambers.