This year marked the 20th anniversary of the Partisan Voter Index (PVI). PVI is a measurement of how partisan a district or state is. It is calculated using results of the last two presidential elections. For example, a district with the score of D+5 means that in the 2012 and 2016 presidential elections, that district performed an average of five points more Democratic than the nation did as a whole.
With 2017 coming to a close, our friends at Quorum analyzed what the PVI of a district can reveal about how often a member of Congress works across the aisle. One of their key findings is that members in less partisan districts vote against their party at a higher rate than a member in more partisan districts.
Quorum found that members in swing districts (D+5 to R+5) vote against their party an average of 7.5% of the time.
Here's a list of the top ten Republicans and Democrats who vote against their parties most often. Many are in some of the least partisan and/or most competitive districts in the country.
Top 10 Democrats
Top 10 Republicans
Check out the full report to see how this pattern carries over to the Senate and bill sponsorship.