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Introducing The Cook Political Report Partisan Voting Index (PVI) for the 111th Congress
April 9, 2009
Cook Partisan Voter Index by State and District
Cook Partisan Voter Index by Member
Cook Partisan Voter Index by Partisan Rank
Cook Partisan Voter Index by State
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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, we have updated these PVI ratings and have even more information to draw upon to understand the congressional level trends and tilts that will help to define upcoming elections.
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 51.3 percent, and that of Republicans, which is roughly 48.7 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 2002 (and additional remaps in Texas and Georgia in 2004 and 2006) made some significant changes to the congressional map that make it hard to compare current districts with their predecessors.
Looking for Trends
Now that we have calculated PVI data over a span of five presidential election cycles, we have a wealth of information to draw upon to look for political trends that will be important in upcoming elections. For example, this chart highlights the fact that there are far fewer swing districts today than there were in the 1990s.
During the 1990s, there were 88 districts where the PVI score was D+10 or more and 70 districts where the PVI was R+10 or more. Only two Republicans were in those D+10 seats and just two Democrats were in the R+10 districts, meaning that there were 154 congressional districts that were essentially locked down for one party or the other. That translated to about 35 percent of all House seats that were essentially safe seats.
The latest PVI ratings from the 2004 and 2008 presidential elections show 111 districts where the PVI score is D+10 or more and 111 districts where the PVI score is R+10 or more. There is only one Republican sitting in those D+10 districts (Joseph Cao of New Orleans) and there are only sixteen Democrats in the R+10 seats, meaning that there are 222 seats essentially locked down for one party of the other. That translates to over half (51 percent) of all congressional districts as non-competitive.
This chart ranks each district from the most Republican (Spencer Bachus’s AL-06 at R+29) to the most Democratic (Jose Serrano's NY-16 at D+41). In the 1992 and 1996 elections, there were 67 districts that most closely mirrored the nation as a whole; those in the D+1.9 to R+1.9 range. In the 2004 and 2008 elections, there were only about half as many of these districts – just 37.
Democrats now hold the lion's share – 34 – of the 50 most potentially competitive districts (those that fall in the R+2 to D+2 category). Many of those seats are suburban districts in the Midwest and East Coast, such as the south Jersey district represented by Rep. John Adler (R+1), the Cincinnati suburbs represented by Rep. Steve Driehaus (D+1), and the Minneapolis suburbs represented by Rep. Erik Paulsen (EVEN).
Nearly half of these 50 seats – 23 – switched from Republican to Democratic control in 2006 or 2008. Many of these districts have been competitive for over a decade, with some interesting exceptions. For example, in the period covering the 1992 and 1996 presidential elections, Rep. Mary Jo Kilroy’s suburban Columbus, Ohio district had a PVI score of R+7 and reliably elected Republican Deborah Pryce to Congress. Its new PVI score of D+1 illustrates that the district is trending more Democratic.
Not surprisingly, the previously Democratic-held districts that changed the most between the presidential elections of the 1990s and 2000s were in the South. Thanks in large part to the appeal of President Clinton, Arkansas' three Democratic-held districts enjoyed high Democratic PVI scores as a result of the 1992 and 1996 elections. But, in 2004 and 2008, the underlying Republican nature of the state, which was masked by Clinton for eight years, emerged. For example, the PVI score for the 1992 and 1996 elections in Democratic Rep. Mike Ross's southern Arkansas 4th CD was D+12. The new PVI score is R+7.
Big Movers
Thanks to a new mountain of data from the 2008 election, there are many districts where the PVI score shifted significantly between the 110th Congress and the 111th Congress. The replacement of 2000 election data with 2008 election data accounts for these big swings, although it should be noted that the national averages we used to calculate PVI changed as well, from a Democratic value of 48.8 percent (Kerry’s share of the two-party vote) to 51.3 percent (Kerry and Obama’s average share of the two-party vote).
Getting More Republican
Here is a list of the 50 districts where Republicans have made the greatest strides in presidential-level performance, as measured by comparing pre-2008 PVI scores to post-2008 scores:
| District | Member | Party | Old PVI | New PVI | Difference |
| AL-04 | Aderholt, Robert B. | R | R+16 | R+26 | 10 pts |
| TN-04 | Davis, Lincoln | D | R+3 | R+13 | 10 pts |
| NY-09 | Weiner, Anthony D. | D | D+14 | D+5 | 9 pts |
| TN-06 | Gordon, Bart | D | R+4 | R+13 | 9 pts |
| OK-02 | Boren, Dan | D | R+5 | R+14 | 9 pts |
| AR-01 | Berry, Marion | D | D+1 | R+8 | 8 pts |
| KY-05 | Rogers, Harold | R | R+8 | R+16 | 8 pts |
| AR-04 | Ross, Mike | D | EVEN | R+7 | 8 pts |
| TN-01 | Roe, Phil | R | R+14 | R+21 | 7 pts |
| LA-03 | Melancon, Charlie | D | R+5 | R+12 | 7 pts |
| WV-03 | Rahall, Nick J., II | D | EVEN | R+6 | 7 pts |
| TN-08 | Tanner, John S. | D | EVEN | R+6 | 7 pts |
| LA-07 | Boustany, Charles W. | R | R+7 | R+14 | 6 pts |
| OK-03 | Lucas, Frank D. | R | R+18 | R+24 | 6 pts |
| FL-19 | Wexler, Robert | D | D+21 | D+15 | 6 pts |
| TN-07 | Blackburn, Marsha | R | R+12 | R+18 | 6 pts |
| AL-05 | Griffith, Parker | D | R+6 | R+12 | 6 pts |
| NY-03 | King, Peter T. | R | D+2 | R+4 | 6 pts |
| NY-08 | Nadler, Jerrold | D | D+28 | D+22 | 6 pts |
| NY-05 | Ackerman, Gary L. | D | D+18 | D+12 | 5 pts |
| PA-12 | Murtha, John P. | D | D+5 | R+1 | 5 pts |
| LA-01 | Scalise, Steve | R | R+18 | R+24 | 5 pts |
| GA-09 | Deal, Nathan | R | R+23 | R+28 | 5 pts |
| FL-20 | Wasserman Schultz, Debbie | D | D+18 | D+13 | 5 pts |
| NY-13 | McMahon, Mike | D | D+1 | R+4 | 5 pts |
| OK-04 | Cole, Tom | R | R+13 | R+18 | 5 pts |
| TN-02 | Duncan, John J. | R | R+11 | R+16 | 5 pts |
| TX-08 | Brady, Kevin | R | R+20 | R+25 | 5 pts |
| NJ-04 | Smith, Christopher H. | R | R+1 | R+6 | 5 pts |
| TN-03 | Wamp, Zach | R | R+8 | R+13 | 5 pts |
| MA-04 | Frank, Barney | D | D+19 | R+14 | 5 pts |
| AR-02 | Snyder, Vic | D | EVEN | R+5 | 5 pts |
| AR-03 | Boozman, John | R | R+11 | R+16 | 5 pts |
| LA-04 | Fleming, John | R | R+7 | R+11 | 4 pts |
| AL-03 | Rogers, Mike | R | R+4 | R+9 | 4 pts |
| LA-05 | Alexander, Rodney | R | R+10 | R+14 | 4 pts |
| KY-01 | Whitfield, Ed | R | R+10 | R+15 | 4 pts |
| NJ-09 | Rothman, Steven R. | D | D+13 | D+9 | 4 pts |
| VA-09 | Boucher, Rick | D | R+7 | R+11 | 4 pts |
| AZ-02 | Franks, Trent | R | R+9 | R+13 | 4 pts |
| TX-04 | Hall, Ralph M. | R | R+17 | R+21 | 4 pts |
| TX-13 | Thornberry, Mac | R | R+25 | R+29 | 4 pts |
| MA-09 | Lynch, Stephen F. | D | D+15 | D+11 | 4 pts |
| MA-06 | Tierney, John F. | D | D+11 | D+7 | 4 pts |
| MA-03 | McGovern, James P. | D | D+13 | D+9 | 4 pts |
| PA-18 | Murphy, Tim | R | R+2 | R+6 | 4 pts |
| NY-04 | McCarthy, Carolyn | D | D+9 | D+6 | 4 pts |
| AL-06 | Bachus, Spencer | R | R+25 | R+29 | 4 pts |
| NJ-06 | Pallone, Frank | D | D+12 | D+8 | 4 pts |
| NY-02 | Israel, Steve | D | D+8 | D+4 | 4 pts |
Leading the pack is GOP Rep. Robert Aderholt’s seat in northern Alabama, which gave Al Gore 37 percent of the vote in 2000 but gave Obama just 22 percent in 2008. Deep South districts like Aderholt’s were heavily contested as recently as the 1990s, but would be out of reach for most Democratic hopefuls today.
Somewhat surprisingly, Democrats currently occupy a majority of the seats on this list, including seven of the top ten. Plenty of these Democrats look safe today thanks to their conservatism and their strong personal appeal. For example, Rep. Dan Boren’s district in eastern Oklahoma gave McCain 66 percent of the vote but simultaneously reelected Boren with 70 percent.
But in a bad year for Democrats, or when seats open up, “ticking time bomb” districts such as these could be worrisome for congressional Democrats. Districts on this list accounted for only one of House Democrats’ 54 pickups between 2006 and 2008; in some places, competing here would have amounted to going seriously against the grain.
It’s also worth noting that these GOP-trending seats aren’t exclusive to the South. The Northeast and South Florida are home to 19 of these districts where Obama seriously underperformed Gore, and in some cases Kerry. New York Rep. Anthony Weiner’s heavily Jewish district was actually a close call for Obama in 2008, even though it is reliably Democratic at the congressional level.
Finally, seven of these districts are in Tennessee, where Gore’s performance in non-major metro areas was significantly higher than Kerry’s and Obama’s. This home-state effect factored into the old PVI, but was not taken into account in the new scores.
Getting More Democratic
Here is a list of the 50 districts where Democrats have made the greatest strides in presidential-level performance, as measured by comparing pre-2008 PVI scores to post-2008 scores:
| District | Member | Party | Old PVI | New PVI | Difference |
| GA-13 | Scott, David | D | D+10 | D+15 | 5 pts |
| IN-07 | Carson, Andre | D | D+9 | D+14 | 5 pts |
| TN-09 | Cohen, Steve | D | D+18 | D+23 | 5 pts |
| NC-12 | Watt, Melvin L. | D | D+11 | D+16 | 4 pts |
| IL-08 | Bean, Melissa L. | D | R+5 | R+1 | 4 pts |
| VT-AL | Welch, Peter | D | D+9 | D+13 | 4 pts |
| HI-02 | Hirono, Mazie K. | D | D+10 | D+14 | 4 pts |
| TX-25 | Doggett, Lloyd | D | D+1 | D+6 | 4 pts |
| TX-24 | Marchant, Kenny R | R | R+15 | R+11 | 4 pts |
| HI-01 | Abercrombie, Neil | D | D+7 | D+11 | 4 pts |
| MT-AL | Rehberg, Dennis R. | R | R+11 | R+7 | 4 pts |
| TX-03 | Johnson, Sam | R | R+17 | R+14 | 3 pts |
| PA-16 | Pitts, Joseph R. | R | R+11 | R+8 | 3 pts |
| IL-06 | Roskam, Peter J. | R | R+3 | EVEN | 3 pts |
| IL-13 | Biggert, Judy | R | R+5 | R+1 | 3 pts |
| IL-14 | Foster, Bill | D | R+5 | R+1 | 3 pts |
| IN-04 | Buyer, Steve | R | R+17 | R+14 | 3 pts |
| TX-10 | McCaul, Michael T. | R | R+13 | R+10 | 3 pts |
| VA-10 | Wolf, Frank R. | R | R+5 | R+2 | 3 pts |
| VA-11 | Connolly, Gerry | D | R+1 | D+2 | 3 pts |
| TX-32 | Sessions, Pete | R | R+11 | R+8 | 3 pts |
| CO-04 | Markey, Betsy | D | R+8 | R+6 | 3 pts |
| TX-07 | Culberson, John Abney | R | R+16 | R+13 | 3 pts |
| NV-02 | Heller, Dean | R | R+8 | R+5 | 3 pts |
| MI-03 | Ehlers, Vernon J. | R | R+9 | R+6 | 3 pts |
| TX-31 | Carter, John R. | R | R+16 | R+14 | 3 pts |
| IN-05 | Burton, Dan | R | R+20 | R+17 | 3 pts |
| CO-01 | DeGette, Diana | D | D+18 | D+21 | 3 pts |
| ND-AL | Pomeroy, Earl | D | R+13 | R+10 | 3 pts |
| CA-06 | Woolsey, Lynn C. | D | D+21 | D+23 | 3 pts |
| CA-01 | Thompson, Mike | D | D+10 | D+13 | 3 pts |
| CO-02 | Polis, Jared | D | D+8 | D+11 | 3 pts |
| TX-21 | Smith, Lamar S. | R | R+16 | R+14 | 3 pts |
| NC-13 | Miller, Brad | D | D+2 | D+5 | 3 pts |
| NE-02 | Terry, Lee | R | R+9 | R+6 | 3 pts |
| VA-08 | Moran, James P. | D | D+14 | D+16 | 2 pts |
| CA-23 | Capps, Lois | D | D+9 | D+12 | 2 pts |
| CA-14 | Eshoo, Anna G. | D | D+18 | D+21 | 2 pts |
| IN-03 | Souder, Mark E. | R | R+16 | R+14 | 2 pts |
| CA-48 | Campbell, John | R | R+8 | R+6 | 2 pts |
| GA-04 | Johnson, Henry C. 'Hank' | D | D+22 | D+24 | 2 pts |
| NM-01 | Heinrich, Martin | D | D+2 | D+5 | 2 pts |
| IL-10 | Kirk, Mark Steven | R | D+4 | D+6 | 2 pts |
| OR-01 | Wu, David | D | D+6 | D+8 | 2 pts |
| IN-02 | Donnelly, Joe | D | R+4 | R+2 | 2 pts |
| IL-16 | Manzullo, Donald A. | R | R+4 | R+2 | 2 pts |
| CO-07 | Perlmutter, Ed | D | D+2 | D+4 | 2 pts |
| UT-02 | Matheson, Jim | D | R+17 | R+15 | 2 pts |
| CA-17 | Farr, Sam | D | D+17 | D+19 | 2 pts |
| OH-15 | Kilroy, Mary Jo | D | R+1 | D+1 | 2 pts |
Compared to the rest of the country, the districts where Obama made the greatest advances versus past Democratic performance were disproportionately western and suburban. New Mexico’s 1st CD, for example, was a classic swing district for over a decade but now tilts Democratic. It strongly supported Obama and new Rep. Martin Heinrich in 2008.
Demographic changes are responsible for new electoral dynamics in many districts on this list. The rapidly increasing African-American percentage in Georgia Rep. David Scott’s south suburban Atlanta district has made it much more Democratic and has shielded Scott from political threats. And a rapidly rising Hispanic population in Dallas-area Rep. Kenny Marchant’s district has boosted Democratic numbers there, although it is still quite safe for the GOP.
If current lines stay more or less the same after 2012 redistricting – and that is a big if – then a handful of these districts could be promising long-term projects for Democrats. Districts currently held by GOP Reps. Joe Pitts of Pennsylvania, Michael McCaul of Texas, and Frank Wolf of Virginia seem to be getting friendlier to Democrats every cycle.
Of course, it should be noted that an Obama home-state effect is a major reason why both Hawaii districts and six suburban Chicago districts appear on this list.
