Changes in the location of the median voter in the US House of Representatives, 1963-1996

We consider the degree of ideological polarization within and between the parties in the U.S. House of Representatives for the period 1963-1996, using the Groseclose, Levitt and Snyder (1996) adjustment method for ADA and ACU scores to ensure over time comparability of roll call voting data. We focus especially on the median House member, since we believe that change in the median offers a better measure of the impact of the change in party control than does changes in the mean roll-call voting score. Our data analysis makes two general points. First and foremost, when we looked at the change in the location of the House median voter, we found a dramatic change after the Republicans gained a majority in the House in 1994. After the Republicans became a majority in the House, the ADA median in the House in 1995-1996 was at 24, far closer to the Republican median of 4 than to the Democratic median of 83. The shift in median from 1993-1994 to 1994-1995 involved a change of over 25 points in one election - far and away the greatest single shift in ideology of the modern era. In contrast, the mean changed only 1 point over this same period. Second, for the three decades we investigated, we found three historical epochs vis a vis the relative locations of the ADA (or ACU) floor median and the ADA (or ACU) floor mean in the U.S. House of Representatives - two inflection points in 1983 and 1994 which are related to trends in regional realignment.