In this piece for the LSE's USAPP blog, I summarize joint work with Mark Duggan, Joe Orsini, and Pietro Tebaldi on how states' choices about the boundaries of their ACA marketplace rating regions shaped insurer entry and premiums in the exchanges' first year. When small, rural counties were bundled into a region with a larger urban neighbor, more insurers entered and benchmark premiums were lower; regions that mix very high and very low levels of urbanity, however, were less attractive to insurers and had higher premiums.

Read the full post here.