105th Congress Fit Statistics



House 2-Dimensional W-NOMINATE Scaling

Total Number of Roll Calls: 1166
Number of Scalable Roll Calls (2.5% Minority or better): 946
Number of Constrained Roll Calls [Midpoint at end of Dimension(s)]: 87
Correct Classification: 1 Dimension: 88.2%, APRE=.644
                                  2 Dimensions: 89.1%, APRE=.674
Geometric Mean Probability: 1 Dimension: .756
                                           2 Dimensions: .774

Senate 2-Dimensional W-NOMINATE Scaling

Total Number of Roll Calls: 612
Number of Scalable Roll Calls (2.5% Minority or better): 486
Number of Constrained Roll Calls [Midpoint at end of Dimension(s)]: 59
Correct Classification: 1 Dimension: 88.0%, APRE=.642
                                  2 Dimensions: 88.5%, APRE=.660
Geometric Mean Probability: 1 Dimension: .751
                                           2 Dimensions: .771

By comparison, the fit of the 104th House was 88.7% correct classification (APRE=.683) and geometric mean of .769 for the first dimension, and 90.0% correct classification(APRE=.717) and geometric mean of .787 for two dimensions. The fit of the 104th Senate was 87.9% correct classification (APRE=.666) and geometric mean of .752, and 88.9% (APRE=.695) and geometric mean of .775 for two dimensions.

These preliminary results show that the trends that we discuss in chapter 11 of Congress: A Political-Economic History of Roll Call Voting (1997, Oxford University Press) and Income Redistribution and the Realignment of American Politics (joint with Nolan McCarty, 1997, AEI Press) are continuing. In the post World War II period only two dimensions are required to account for the great bulk of roll call voting. The primary dimension is the liberal-conservative dimension so familiar to students of politics and epitomized by voting on the basic issue of the role of government in the economy. The second dimension captures the conflict over race and civil rights. However, with the passage of the 1964 Civil Rights Act, the 1965 Voting Rights Act, and the 1967 Open Housing Act, this second dimension has slowly declined in importance. Race related issues affirmative action, welfare, Medicaid, subsidized housing, etc. are now questions of redistribution. Voting on race related issues now largely takes place along the liberal-conservative dimension and the old split in the Democratic party between North and South has largely disappeared. Consequently, since the mid-1970s, American politics has become increasingly polarized around a left-right conflict along party lines.