The House party gap widened from 0.52 to 0.91 since 1947

Source. Voteview, DW-NOMINATE dimension 1, party means

Method and data

Method. Gap is the Republican mean minus the Democratic mean of nominate_dim1 for party codes 200 and 100, President rows excluded, one point per Congress, plotted at its first year. House means include Delegates and the Resident Commissioner; dropping them moves a House gap by at most 0.002, and dropping House members with 13 or fewer votes by at most 0.003, in the Congresses tested. Senate means use party codes 100 and 200 only, so independents (code 328) are in neither mean; counting them as Democrats moves a Senate gap by at most 0.012. The exhibit starts in 1947; the same file extends the series to the 34th Congress (1855).

Congress	First year	House gap	Senate gap	House Democratic mean	House Republican mean	Senate Democratic mean	Senate Republican mean
80	1947	0.522669	0.484316	−0.237325	0.285344	−0.191532	0.292784
81	1949	0.552575	0.505925	−0.275569	0.277006	−0.239393	0.266532
82	1951	0.542353	0.476333	−0.262333	0.280019	−0.200333	0.276
83	1953	0.531002	0.478589	−0.253344	0.277658	−0.191792	0.286796
84	1955	0.556349	0.510725	−0.279098	0.277251	−0.230235	0.280489
85	1957	0.551	0.501816	−0.282779	0.268221	−0.233962	0.267854
86	1959	0.562428	0.528392	−0.29571	0.266718	−0.272448	0.255944
87	1961	0.539655	0.546842	−0.277286	0.262369	−0.277892	0.26895
88	1963	0.548062	0.569598	−0.292046	0.256017	−0.291174	0.278424
89	1965	0.546589	0.576847	−0.300764	0.245825	−0.297271	0.279576
90	1967	0.538546	0.551906	−0.29552	0.243026	−0.298906	0.253
91	1969	0.564391	0.539893	−0.309768	0.254623	−0.289052	0.250841
92	1971	0.564948	0.519972	−0.310548	0.2544	−0.28675	0.233222
93	1973	0.584411	0.590679	−0.323467	0.260944	−0.325842	0.264837
94	1975	0.580316	0.595383	−0.315289	0.265027	−0.324541	0.270842
95	1977	0.573078	0.588672	−0.305915	0.267163	−0.319646	0.269026
96	1979	0.59613	0.589499	−0.301335	0.294795	−0.312864	0.276634
97	1981	0.606964	0.60986	−0.300433	0.306531	−0.299304	0.310556
98	1983	0.62744	0.608708	−0.301757	0.325683	−0.301326	0.307382
99	1985	0.643289	0.619762	−0.309498	0.333791	−0.305596	0.314167
100	1987	0.644612	0.608429	−0.309271	0.335341	−0.294364	0.314065
101	1989	0.652637	0.61645	−0.312992	0.339644	−0.293429	0.323022
102	1991	0.65888	0.618991	−0.314144	0.344735	−0.299172	0.319818
103	1993	0.7048	0.633965	−0.333828	0.370972	−0.296298	0.337667
104	1995	0.757875	0.652859	−0.361264	0.39661	−0.30175	0.351109
105	1997	0.77713	0.684119	−0.375575	0.401554	−0.310356	0.373764
106	1999	0.776811	0.658585	−0.372789	0.404022	−0.294674	0.363911
107	2001	0.786356	0.66354	−0.37672	0.409636	−0.29468	0.36886
108	2003	0.792966	0.649523	−0.376221	0.416745	−0.291896	0.357627
109	2005	0.809919	0.685679	−0.387158	0.422762	−0.307733	0.377945
110	2007	0.807746	0.686509	−0.368305	0.439442	−0.29494	0.391569
111	2009	0.805008	0.705295	−0.348823	0.456186	−0.308545	0.39675
112	2011	0.860434	0.744081	−0.39325	0.467184	−0.300226	0.443854
113	2013	0.866044	0.795738	−0.384377	0.481667	−0.325912	0.469826
114	2015	0.874343	0.809204	−0.394442	0.4799	−0.333	0.476204
115	2017	0.877509	0.821865	−0.388465	0.489044	−0.334938	0.486927
116	2019	0.871986	0.841585	−0.371779	0.500207	−0.342696	0.498889
117	2021	0.881785	0.877571	−0.379207	0.502578	−0.352061	0.52551
118	2023	0.892257	0.894906	−0.384118	0.508139	−0.350538	0.544367
119	2025	0.909968	0.922608	−0.38636	0.523608	−0.367222	0.555386

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