The R-2=.93: Where then do they differ? Comparing liberal and conservativeinterest group ratings

Interest group ratings have long been used by social scientists to distingu ish between liberal and conservative members of Congress. It is also well k nown that ratings by different groups are highly correlated with one anothe r. Here, rather than focusing on the similarities between such measures, we focus on the differences between them. Although the relationship between m easures is nearly linear, we find systematic robust differences between Ame ricans for Democratic Action (ADA) and American Conservative Union (ACU) sc ores. Using a variety of techniques, we show that interest groups are most interested in distinguishing among their ideological friends and tend to gr oup 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 impa ct of ideology on such phenomena. Finally, we propose and test a method tha t corrects for this bias.