Could a Changing Distribution of Roll Call Margins Account for the Polarization?
• To test this we re-ran DW-NOMINATE for the 1st through the 105th Congresses constraining each House to have the same distribution of roll call margins. The average distribution of margins for all 105 Houses was used as the common margin and the number of roll calls for each House was set equal to 400. The distribution is shown below: C C ROLL CALL WEIGHTS C 1 50 – 55 92 0.23 2 56 – 60 80 0.20 3 61 – 65 60 0.15 4 66 – 70 44 0.11 5 71 – 75 32 0.08 6 76 – 80 24 0.06 7 81 – 85 20 0.05 8 86 – 90 16 0.04 9 91 – 95 20 0.05 10 96 – 97.5 12 0.13 To construct the artificial data for each House we sampled each margin category with replacement to get the required number. For example, if for some House there were 75 roll calls with margins in the range 66 – 70 then 44 roll calls from those 75 were drawn with replacement. If there were no roll calls in the range then no roll calls could be included. Hence, there are a few Houses with fewer than 400 roll calls. For example, the 58th House had no ro
• To test this we re-ran DW-NOMINATE for the 1st through the 105th Congresses constraining each House to have the same distribution of roll call margins. The average distribution of margins for all 105 Houses was used as the common margin and the number of roll calls for each House was set equal to 400. The distribution is shown below: C C ROLL CALL WEIGHTS C 1 50 – 55 92 0.23 2 56 – 60 80 0.20 3 61 – 65 60 0.15 4 66 – 70 44 0.11 5 71 – 75 32 0.08 6 76 – 80 24 0.06 7 81 – 85 20 0.05 8 86 – 90 16 0.04 9 91 – 95 20 0.05 10 96 – 97.5 12 0.13 To construct the artificial data for each House we sampled each margin category with replacement to get the required number. For example, if for some House there were 75 roll calls with margins in the range 66 – 70 then 44 roll calls from those 75 were drawn with replacement. If there were no roll calls in the range then no roll calls could be included. Hence, there are a few Houses with fewer than 400 roll calls. For example, the 58th House had no ro
