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Is the Democratic Party 'Overrepresented' in the U.S. House?

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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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1 Comment


  • Interesting. I assume the reverse is true in the Senate, with a large number of plains/western red state senators representing a small number of voters?

  • Leave a comment


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