The dynamics of interest group evaluations of Congress

We apply a dynamic spatial model to interest group ratings of the members o f Congress over the period 1959-1981. Spatial distances between an interest group and the members of Congress are assumed to be monotonic with the rat ings. Our pooled cross-sectional time-series data set consists of 203,387 r atings by 59 interest groups. We restrict the spatial coordinates of the in terest groups and members of Congress to be polynomial functions of time. T wo significant dimensions are recovered: the first dimension, which account s for approximately 75% of the variance, represents liberal-conservative po sitions on economic issues; the second dimension, which accounts for approx imately an additional 5% of the variance, represents liberal-conservative p ositions on social issues. Nearly all the interest groups and most members of Congress are ideologically consistent. They are either liberal on both d imensions or conservative on both.