"Unintentional Gerrymandering"

The New York Times reports:

The latest round of redistricting is not the only reason Republicans lost the popular vote but won a majority of House seats, several political scientists and analysts said. Incumbency is a powerful weapon, they noted, and Republicans went into the election with a big majority in the House. A new election process in California pitted some Democrats against one another in the general election.

And a number of political scientists pointed to what Jowei Chen, an assistant professor of political science at the University of Michigan, and Jonathan Rodden, a professor of political science at Stanford University, call “unintentional gerrymandering” in a forthcoming paper — the natural geographic patterns that lead many Democrats to choose to live in dense, urban areas with very high concentrations of Democrats, effectively packing themselves into fewer districts.

“Now, more than ever in history, Democrats are clustered in a small number of these urban districts,” Professor Chen said in an interview.

But it is undeniable that redistricting played a role as well. The new lines helped Republicans maintain their control of the House, largely because they were able to add more Republican voters to districts where Republicans won close races in 2010.