Is the Democratic Party ‘Overrepresented’ in the U.S. House?

Democratic candidates have won 772 more U.S. House seats since 1942 than their cumulative ‘proportional vote share,’ or 23 seats per election cycle; +27 seats in 2008

The Republican Party has received the most attention – and criticism – in recent years for its efforts to redraw district lines to benefit their own party (e.g. the Tom Delay-backed 2003 Texas redistricting plan).

However, a new Smart Politics study of nearly 15,000 U.S. House elections since 1942 finds it is the Democratic Party that historically (and currently) has profited the most from the geographic twists and turns that define the nation’s 435 Congressional District lines every ten years.

Smart Politics compared the cumulative vote percentage for Democratic and Republican candidates respectively in the 14,792 general election U.S. House contests conducted across the 34 election cycles since 1942 to the percentage of seats won by each party during each of those cycles.

In total, the Democratic Party has won 772 more seats than their ‘proportional vote share,’ or an average of +22.7 seats per election cycle.

Republicans, meanwhile, have won 410 seats less than their proportional share of votes cast for U.S. House candidates, or an average of -12.1 seats per election cycle.

Of course, seats are allocated on a winner-take-all basis in U.S. elections, so no party is entitled to a proportional share of the seats in Congress.

That said, it is an ideal of a democratic society that district lines drawn across the country (usually by state legislatures) should be created without regard to enhancing the partisan advantage of the party in power.

Many researchers have shown that the common denominator across all the states when determining how new district plans are drawn up is that it protects incumbents – often regardless of party.

However, the data generated in this report demonstrates that it is the Democratic Party that has inordinately benefited from the lines than have been drawn over the decades.

In all but four election cycles (1946, 1952, 1996, and 2004), the percentage of U.S. House seats won by Democrats was greater than the cumulative percentage of votes cast for their candidates on Election Day.

For example, in 2008, Democrats won 52.9 percent of the votes cast for U.S. Representatives across the nation’s 435 Congressional Districts. However, the Democratic Party won 59.1 percent of the seats in Congress (257) – or 27 more seats in their favor than if their seats had been allotted based on a ‘proportional share’ of the vote (230).

Republicans, meanwhile, won 42.4 percent of the vote in 2008. However, the GOP won just 40.9 percent of the seats in Congress – or 6 seats fewer than their ‘proportional share’ (178 vs. 184).

(Note: the ‘proportional total’ of Democratic and Republican seats does not sum to 435 due to the fact that third party and independent candidates usually receive between 2 and 6 percent of the vote in U.S. House contests nationwide each election cycle. A second analysis, which found similar results, is conducted later in this report examining the proportional two-party share of Democratic and Republican U.S. House votes received and seats won.

Overall, district lines seem to have been drawn to the detriment of the Republican Party over the years. The percentage of seats won by Republicans has been less than the percentage of votes cast for Republican U.S. House candidates in 25 of the last 34 election cycles, including 24 of 26 cycles from 1942-1992.

And while the GOP did receive a disproportionate advantage over the Democrats in seats won vis-à-vis votes cast for their candidates from 1996 through 2006, the advantage was scant compared to that enjoyed by the Democrats from the 1940s through the early 1990s.

U.S. House Seats Won by Party vs. ‘Proportional Share’ of Seats Based on Party’s Cumulative Percentage of the Vote, 1942-2008

Year	D-Seats	D-Prop.	D-Diff.	R-Seats	R-Prop.	R-Diff.
2008	257	230	+27	178	184	-6
2006	233	226	+7	202	192	+10
2004	202	203	-1	232	214	+18
2002	205	195	+10	229	215	+14
2000	212	204	+8	221	206	+15
1998	211	205	+6	223	209	+14
1996	206	209	-3	228	208	+20
1994	204	195	+9	230	224	+6
1992	258	217	+41	176	195	-19
1990	267	226	+41	167	191	-24
1988	260	232	+28	175	197	-22
1986	258	235	+23	177	192	-15
1984	253	226	+27	182	203	-21
1982	269	239	+30	166	188	-22
1980	242	219	+23	192	207	-15
1978	277	232	+45	158	194	-36
1976	292	242	+50	143	183	-40
1974	291	248	+43	144	176	-32
1972	242	225	+17	192	202	-10
1970	255	231	+24	180	193	-13
1968	243	217	+26	192	210	-18
1966	247	219	+28	187	208	-21
1964	295	248	+47	140	184	-44
1962	259	227	+32	176	205	-29
1960	263	237	+26	174	196	-22
1958	283	242	+41	153	191	-38
1956	234	220	+14	201	212	-11
1954	232	227	+5	203	205	-2
1952	213	214	-1	221	215	+6
1950	235	213	+22	199	213	-14
1948	263	224	+39	171	197	-26
1946	188	193	-5	246	233	+13
1944	242	220	+22	191	205	-14
1942	222	200	+22	209	220	-11
Total	8,313	7,541	+772	6,458	6,868	-410

Data compiled by Smart Politics.

There are some theoretical alternative explanations, of course, for why Democrats have apparently benefited inordinately across the decades in terms of the allocation of seats in Congress versus the percentage of votes won.

For example, if Democratic candidates won a significantly greater number of their seats by close margins compared to the Republicans, that would help to drive the proportional imbalance, as millions of Republican votes cast in close races would not be generating any actual seats won in Congress.

However, this theory does not hold up, at least in the current redistricting cycle:

· Since 2002, Democrats and Republicans have won virtually an identical number of “competitive” elections, or those decided by less than 10 points. Democrats have won 80 while the Republicans have won 81.

· Moreover, it is the Democratic Party which has been on the winning end of many more blow-out elections than the GOP. For example, from 2002 to 2008, the Democratic Party held 43 of the 50 least competitive seats in the nation (districts with the largest margin of victories).

· Democrats have also racked up vote totals against the GOP by running without a Republican opponent in 153 races since 2002, compared to just 105 races in which the Republican candidate did not face a Democratic challenger.

An analysis based on the proportional allocation of seats vis-à-vis the two-party vote share reveals similar results with the Democratic Party enjoying a significant disproportionate advantage in terms of seats won versus votes received.

Under these metrics, Democrats won 585 more seats (and Republicans 585 fewer seats) across the 34 election cycles than their proportional share of the two-party vote, or 17.2 seats per election cycle (with Republicans at -17.2).

In the 2008 election, for example, Democrats won a cumulative 55.5 percent of the two-party vote, with Republicans at 44.5 percent. If Democrats had been allotted a ‘proportional’ 55.5 percent share of U.S. House seats, they would have won 242 seats, not the 257 they notched on Election Day. Similarly, the GOP would have ended up with 193 seats instead of 178.

While the GOP did reap a disproportionate share of the seats in Congress from 1996 through 2006 under this two-party vote share, their average advantage of +5.3 seats was comparatively meager to what the Democrats reaped in 2008 (+15 seats) or through most of the 1940s (+14.5 seats), 1950s (+13.8 seats), 1960s (+29.2 seats), 1970s (+30.6 seats), 1980s (+22.4 seats), and early 1990s (+12.6 seats).

Democratic Seats Won vs. Seats Allocated by Proportional Two-Party Vote Share in U.S. House Elections, 1942-2008

Year	D-seats	R-seats	D-Prop.	R-Prop.	D-Advantage
2008	257	178	242	193	+15
2006	233	202	235	200	-2
2004	202	232	211	223	-9
2002	205	229	206	228	-1
2000	212	221	216	217	-4
1998	211	223	215	219	-4
1996	206	228	218	216	-12
1994	204	230	202	232	+2
1992	258	176	229	205	+29
1990	267	167	235	199	+32
1988	260	175	235	200	+25
1986	258	177	240	195	+18
1984	253	182	229	206	+24
1982	269	166	244	191	+25
1980	242	192	223	211	+19
1978	277	158	237	198	+40
1976	292	143	247	188	+45
1974	291	144	255	180	+36
1972	242	192	229	205	+13
1970	255	180	237	198	+18
1968	243	192	222	213	+21
1966	247	187	222	212	+25
1964	295	140	249	186	+46
1962	259	176	228	207	+31
1960	263	174	239	198	+24
1958	283	153	244	192	+39
1956	234	201	222	213	+12
1954	232	203	229	206	+3
1952	213	221	217	217	-4
1950	235	199	217	217	+18
1948	263	171	231	203	+32
1946	188	246	197	237	-9
1944	242	191	224	209	+18
1942	222	209	205	226	+17
Total	8,313	6,458	7,728	7,043	+585

Note: Table reflects the proportional two-party share of seats in the U.S. House based on the cumulative two-party share of votes cast for U.S. Representatives. The two-party seat total is based on total number of seats in Congress less any seats won by independent or third-party candidates (21 seats in total over these 34 election cycles) and any vacancies on Election Day. Data compiled by Smart Politics.

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