House: Partisan Voting Index

The Cook Political Report is pleased to introduce our new 2012 Partisan Voter Index (PVI) for all 435 newly redrawn Congressional districts in the country, compiled especially for the Report by POLIDATA®. First introduced in 1997, the Cook PVI measures how each district performs at the presidential level compared to the nation as a whole. Up until this week, we had used preliminary PVI estimates to gauge the competitiveness of newly drawn seats. But this much more complete data set provides a powerful tool to compare today's array of districts with that of cycles past, view the partisan rank order of districts, and determine redistricting's winners and losers.

Unfortunately for Democrats, this year's index tells a dire story of what can happen when a party suffers an ugly election cycle right before redistricting. Democrats couldn’t have picked a worse year to than 2010 to get clobbered: they lost not only 63 House seats but also more than 680 state legislative seats – empowering Republicans to draw ten-year maps in four times as many districts as Democrats. As a result, thanks to effective GOP cartography, the number of “strong” Republican seats has jumped from 182 to 190 and the number of “strong” Democratic seats has fallen from 150 to 146. Meanwhile, the number of "swing" seats has fallen below 100 for the first time, from 104 to 99.

If both parties hold all their “strong” districts, Democrats would now need to win 73 percent of all “swing” districts to achieve a majority – a very difficult feat even in a “wave” year, something 2012 does not appear to be. It also doesn’t help Democrats that of the 99 “swing seats” (those between D+5 and R+5 in the PVI), 56 lean slightly to Republicans while just 43 lean slightly to Democrats. If every single seat elected a member consistent with its PVI score, there would be 246 Republicans and 189 Democrats, not far off from the current count in the House. This suggests that in a “neutral” year, Democrats could win just as many popular votes for House as the GOP and still fall more than two dozen seats shy of a majority.

Subscribers can view the full 2012 Partisan Voter Index in three different formats below:

2012 Partisan Voter Index by State and District »
2012 Partisan Voter Index by Member Name »
2012 Partisan Voter Index by Partisan Rank »

Before and After Redistricting: Partisan Distribution of the House

In many respects, observing House Democrats trying to take back their majority is like watching a soccer team play an evenly matched opponent when the field is slanted 15 degrees against them. Before redistricting, Republicans started out with 182 “strong” seats, 36 short of a majority. After GOP-dominated redistricting, there are 190 seats with a PVI score of R+5 or greater, requiring them to win merely 28 of 56 “moderately” or “barely” GOP seats to keep their majority.

A look at the partisan distribution of House seats before and after redistricting illustrates how effectively Republicans played “keep-away” in the states they controlled. Rather than drawing hyper-aggressive maps, they placed an emphasis on turning moderately Republican seats into strongly Republican seats. They also eliminated Democratic seats in states that lost seats – Michigan, Missouri, and Pennsylvania to name a few – and dropped the number of “strong” Democratic seats from 150 to 146.

Redistricting Before & After: Partisan Distribution of the House

District Type	Before Redistricting	After Redistricting	Difference
Strongly Republican (R+5 or Greater)	182	190	+8
Moderately Republican (R+2 to R+5)	38	33	-5
Barely Republican (EVEN to R+2)	20	23	+3
Total Republican	240	246	+6
Barely Democratic (EVEN to D+2)	17	12	-5
Moderately Democratic (D+2 to D+5)	28	31	+3
Strongly Democratic (D+5 or Greater)	150	146	-4
Total Democratic	195	189	-6

The Decline of the "Swing Seat"

The most striking House statistic in the last 15 years may be the decline of competitive districts, places where members have the most incentives to work on a bipartisan basis. In 1998, our Partisan Voter Index scored 164 districts between D+5 and R+5, more than a third of the House, and greater than both the number of strongly Democratic and strongly Republican seats. After 2012 redistricting, there are only 99 districts between D+5 and R+5 – less than a quarter of the House and a 40 percent decline since 1998.

Not all of the swing seat decline is attributable to redistricting. In many minimally altered districts, the local electorate has simply become much more homogenous. For example, the boundaries of West Virginia’s 2nd CD haven’t changed much since 1998, but its PVI score has shifted from EVEN to R+8 as voters have moved away from the national Democratic brand. Likewise, Albuquerque’s migration to the left has bumped the PVI score of New Mexico’s 1st CD from R+1 to D+5 in ten years.

But voter self-sorting has also enabled partisan gerrymanderers to more easily polarize districts wherever they wield power over the map. As Robert Draper astutely observed in The Atlantic, the goal of partisan mapmakers is often to “design wombs” for your team and “tombs for the other guys.” But in the case of Northern Virginia’s 11th CD, Republicans actually boosted Democratic Rep. Gerry Connolly’s PVI from D+2 to D+7 in order to make neighboring districts more Republican.

One exception to this dramatic polarization of districts has been California, where a new nonpartisan, citizen-driven redistricting process boosted the number of seats between D+5 and R+5 from eight to 14 overnight. Another exception is New York, where a court-drawn map increased the count of such seats from 11 to 12. But in the remainder of the country, the number of swing seats fell 11 percent, from 82 to 73. The below chart illustrates the overall swing seat trend line between 1998 and 2012:

This chart provides a more detailed look at the partisan breakdown of seats heading into the 2000 election versus where we are today:

Partisan Voter Index (PVI) Summary

1992/1996 Summary: Going Into the 2000 Election

Democratic-Held Seats
D+10.0 or Greater	D+5.0 to D+9.9	D+2.0 to D+4.9	D+1.9 to R+1.9	R+2.0 to R+4.9	R+5.0 to R+9.9	R+10.0 or Greater
77	40	34	31	15	12	2
Republican-Held Seats
D+10.0 or Greater	D+5.0 to D+9.9	D+2.0 to D+4.9	D+1.9 to R+1.9	R+2.0 to R+4.9	R+5.0 to R+9.9	R+10.0 or Greater
4	2	9	37	38	60	74
Totals
D+10.0 or Greater	D+5.0 to D+9.9	D+2.0 to D+4.9	D+1.9 to R+1.9	R+2.0 to R+4.9	R+5.0 to R+9.9	R+10.0 or Greater
81	42	43	68	53	72	76
123		164			148

2004/2008 Summary: Going Into the 2012 Election

Democratic-Held Seats
D+10.0 or Greater	D+5.0 to D+9.9	D+2.0 to D+4.9	D+1.9 to R+1.9	R+2.0 to R+4.9	R+5.0 to R+9.9	R+10.0 or Greater
104	38	26	11	0	9	5
Republican-Held Seats
D+10.0 or Greater	D+5.0 to D+9.9	D+2.0 to D+4.9	D+1.9 to R+1.9	R+2.0 to R+4.9	R+5.0 to R+9.9	R+10.0 or Greater
0	4	5	24	33	59	117
Totals
D+10.0 or Greater	D+5.0 to D+9.9	D+2.0 to D+4.9	D+1.9 to R+1.9	R+2.0 to R+4.9	R+5.0 to R+9.9	R+10.0 or Greater
104	42	31	35	33	68	122
146		99			190

The "Median District" and PVI Rankings

Another way of gauging the impact of redistricting is the concept of the “median district.” Because the Democratic vote tends to be more geographically concentrated in “safe” seats than the Republican vote, the median House district has always leaned slightly Republican since we introduced the Partisan Voter Index. In 1998, the median district was Washington’s 8th CD, held by suburban Seattle GOP Rep. Jennifer Dunn, which was one point more Republican than the national average.

Over the last four years, the median district was Wisconsin’s 1st CD, held by none other than Rep. Paul Ryan, with a PVI score of R+2. Today, the median district is that of Michigan GOP Rep. Tim Walberg, whose 7th CD has a PVI score of R+3. By comparison, the most Republican district in the country is now Amarillo’s TX-13, with a score of R+29, while the most Democratic district is still the Bronx’s NY-15, with a PVI score of D+41.

The “median district” has crept rightward by about two points since 1998. Not only has the Democratic vote become even more concentrated since the mid-1990s; Republicans have also used the redistricting process to “raise the bar” Democrats would need to clear to win a majority. Whereas the House used to be a more level playing field, Democrats could now win every single seat up to R+2 and still fall short of a House majority.

The Median & Most Partisan Districts, 1998-2012

PVI Year	Most Democratic	Median Seat	Most Republican
1998	NY-15: Rangel (D+38)	WA-08: Dunn (R+1)	TX-19: Combest (R+26)
2000	NY-16: Serrano (D+42)	CA-23: Capps (R+1)	TX-19: Combest (R+29)
2002	NY-16: Serrano (D+44)	MI-11: McCotter (R+2)	TX-08: Brady (R+28)
2004	NY-16: Serrano (D+43)	TX-15: Hinojosa (R+2)	UT-03: Cannon (R+27)
2006	NY-16: Serrano (D+43)	AZ-08: Giffords (R+2)	UT-03: Cannon (R+27)
2008	NY-16: Serrano (D+41)	WI-01: Ryan (R+2)	AL-06: Bachus (R+29)
2010	NY-16: Serrano (D+41)	WI-01: Ryan (R+2)	AL-06: Bachus (R+29)
2012	NY-15: Serrano (D+41)	MI-07: Walberg (R+3)	TX-13: Thornberry (R+29)

Before and After Redistricting: Winners and Losers

The two charts below provide a look at which districts underwent the most dramatic alterations in redistricting. While the top 25 most dramatic swings against the incumbent party were fairly even between the two parties (14 Democratic and 11 Republican seats), Republicans were the clear beneficiaries where districts swung in favor of the incumbent party: 19 Republican seats experienced dramatic performance boosts compared to just six Democratic districts.

25 Biggest Redistricting Swings Favoring the Incumbent Party

19 Republican, 6 Democratic

Rank	District	Incumbent	PVI Before	PVI After	Swing	Current Cook Rating
1	TX-27	Blake Farenthold (R)	R+2	R+13	+10.65	Solid Republican
2	WA-09	Adam Smith (D)	D+5	D+15	+10.36	Solid Democratic
3	PA-17	Tim Holden (D)*	R+6	D+4	+10.35	Solid Democratic
4	PA-11	Lou Barletta (R)	D+4	R+6	+10.19	Solid Republican
5	AZ-04	Paul Gosar (R)	R+6	R+16	+9.93	Solid Republican
6	NY-26	Brian Higgins (D)	D+4	D+13	+9.73	Solid Democratic
7	TN-08	Stephen Fincher (R)	R+6	R+15	+9.27	Solid Republican
8	OH-12	Pat Tiberi (R)	D+1	R+8	+9.14	Solid Republican
9	NC-02	Renee Ellmers (R)	R+2	R+11	+8.85	Solid Republican
10	LA-06	Bill Cassidy (R)	R+10	R+19	+8.75	Solid Republican
11	OH-15	Steve Stivers (R)	D+1	R+6	+7.21	Solid Republican
12	NJ-12	Rush Holt (D)	D+5	D+12	+7.00	Solid Democratic
13	OH-01	Steve Chabot (R)	D+1	R+6	+6.95	Solid Republican
14	CO-04	Cory Gardner (R)	R+6	R+12	+6.60	Solid Republican
15	CA-42	Ken Calvert (R)	R+6	R+12	+6.33	Solid Republican
16	SC-02	Joe Wilson (R)	R+9	R+14	+5.08	Solid Republican
17	Fl-17	Tom Rooney (R)	R+5	R+10	+5.03	Solid Republican
18	IL-06	Peter Roskam (R)	EVEN	R+5	+5.03	Solid Republican
19	VA-11	Gerry Connolly (D)	D+2	D+7	+4.99	Solid Democratic
20	WA-08	Dave Reichert (R)	D+3	R+2	+4.84	Solid Republican
21	PA-06	Jim Gerlach (R)	D+4	R+1	+4.82	Likely Republican
22	IL-14	Randy Hultgren (R)	R+1	R+6	+4.69	Solid Republican
23	GA-08	Austin Scott (R)	R+10	R+15	+4.64	Solid Republican
24	WA-02	Rick Larsen (D)	D+3	D+8	+4.27	Solid Democratic
25	FL-10	Dan Webster (R)	R+2	R+7	+4.13	Lean Republican

*Denotes incumbent not currently seeking reelection

25 Biggest Redistricting Swings Against the Incumbent Party

14 Democratic, 11 Republican

Rank	District	Incumbent	PVI Before	PVI After	Swing	Current Cook Rating
1	MD-06	Roscoe Bartlett (R)	R+13	D+2	-15.72	Likely Democratic
2	NC-13	Brad Miller (D)*	D+5	R+9	-14.55	Likely Republican
3	CA-31	Gary Miller (R)	R+10	D+2	-11.65	Solid Republican
4	NY-25	Louise Slaughter (D)	D+15	D+5	-10.68	Likely Republican
5	GA-12	John Barrow (D)	D+1	R+9	-10.57	Lean Republican
6	CA-03	John Garamendi (D)	D+11	D+1	-10.29	Likely Democratic
7	TX-14	Ron Paul (R)*	R+18	R+8	-9.83	Likely Republican
8	NC-08	Larry Kissell (D)	R+2	R+12	-9.49	Lean Republican
9	CA-24	Lois Capps (D)	D+12	D+3	-8.60	Lean Democratic
10	IL-13	Tim Johnson (R)*	R+6	D+1	-7.40	Toss Up
11	MI-09	Sander Levin (D)	D+12	D+5	-7.13	Solid Democratic
12	CO-06	Mike Coffman (R)	R+8	R+1	-6.92	Toss Up
13	IL-11	Judy Biggert (R)	R+1	D+5	-6.55	Toss Up
14	IL-08	Joe Walsh (R)	R+1	D+6	-6.42	Likely Democratic
15	CA-26	Elton Gallegly (R)*	R+4	D+2	-6.10	Toss Up
16	WA-01	Jay Inslee (D)*	D+9	D+3	-5.89	Lean Democratic
17	NC-11	Heath Shuler (D)*	R+6	R+12	-5.72	Likely Republican
18	NC-07	Mike McIntyre (D)	R+5	R+11	-5.46	Toss Up
19	IL-03	Dan Lipinski (D)	D+11	D+5	-5.36	Solid Democratic
20	IN-02	Joe Donnelly (D)*	R+2	R+7	-4.70	Likely Republican
21	IA-04	Steve King (R)	R+9	R+4	-4.64	Lean Republican
22	CA-52	Brian Bilbray (R)	R+3	D+1	-4.28	Toss Up
23	CA-10	Jeff Denham (R)	R+9	R+5	-4.05	Toss Up
24	MA-04	Barney Frank (D)*	D+14	D+11	-3.69	Solid Democratic
25	NY-17	Nita Lowey (D)	D+9	D+5	-3.42	Solid Democratic

*Denotes incumbent not currently seeking reelection

The Cook Political Report Partisan Voter Index (PVI) Explained

In August of 1997, The Cook Political Report introduced the Partisan Voting Index (PVI) as a means of providing a more accurate picture of the competitiveness of each of the 435 congressional districts. Using the 1992 and 1996 major-party Presidential voting results, the PVI measured how each congressional district performed compared to the nation as a whole.

Using the results of the 2004 and 2008 elections for newly drawn Congressional boundaries taking effect in 2012, we have updated these PVI scores and have even more information to draw upon to understand the congressional level trends and tilts that will help to define the elections in 2012 and beyond. We will update PVI scores again in 2013 to reflect the results of the 2012 presidential election.

Developed for The Cook Political Report by Polidata, the index is an attempt to find an objective measurement of each congressional district that allows comparisons between states and districts, thereby making it relevant in both mid-term and presidential election years.

While other data such as the results of senatorial, gubernatorial, congressional and other local races can help fine tune the exact partisan tilt of a particular district, those kinds of results don't allow a comparison of districts across state lines. Only presidential results allow for total comparability.

A Partisan Voting Index score of D+2, for example, means that in the 2004 and 2008 presidential elections, that district performed an average of two points more Democratic than the nation did as a whole, while an R+4 means the district performed four points more Republican than the national average. If a district performed within half a point of the national average in either direction, we assign it a score of EVEN.

To determine the national average for these latest ratings, we have taken the average Democratic share of the two-party presidential vote for 2004 and 2008, which is roughly 51.2 percent, and that of Republicans, which is roughly 48.8 percent. So, if John Kerry captured 55 percent of the vote in a district and Barack Obama carried 57 percent in the district four years later, the district would have a PVI score of roughly D+5.

In addition to the charts above, we have listed the PVI score for every district on the House Race At-A-Glance chart and on each individual race page. It is important to remember that redistricting in 2012 made some significant changes to the congressional map that make it hard to compare current districts with their predecessors.

Notes About PVI Data & Methodology

Following each election and round of redistricting, presidential results are compiled to generate PVI scores for each congressional district. In a few states, these results are aggregated by district by state and/or local election authorities. However, in others they are not, and the reported election results do not account for some votes that are reported centrally and not redirected back to the voter’s registration precinct.

Clark Bensen of Polidata has offered both a detailed explanation of Polidata's methodology for allocating these votes and cautionary notes on the districts for which 2004 and 2008 raw vote totals are still under review. Recalculating presidential results by district following redistricting involves many judgment calls, and while this dataset reflects Polidata's best efforts, raw vote data are preliminary and subject to change upon further post-election review.