THOMAS L. BRUNELL, WILLIAM KOETZLE, JOHN DINARDO,
BERNARD GROFMAN, AND SCOTT L. FELD
The R2 = .93: Where Then Do They Differ?
Comparing Liberal and Conservative Interest Group Ratings
Legislative Studies Quarterly XXIV:87-101

Interest group ratings have long been used by social scientists to distinguish between liberal and conservative members of Congress. It is also well known that ratings by different groups are highly correlated with one another. Here, rather than focusing on the similarities between such measures, we focus on the differences between them. Although the relationship between measures is nearly linear, we find systematic robust differences between Americans for Democratic Action (ADA) and American Conservative Union (ACU) scores. Using a variety of techniques, we show that interest groups are most interested in distinguishing among their ideological friends and tend to group their ideological enemies near the bottom of the scale. Because of this, using any single interest group score to explain political phenomena (i.e., party loyalty) is likely to produce an inconsistent estimate of the impact of ideology on such phenomena. Finally, we propose and test a method that corrects for this bias.


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