This policy brief, drawing on joint work with Mark Duggan, Joe Orsini, and Pietro Tebaldi, examines how states' choices about the geographic boundaries of their ACA marketplace rating regions affected insurer entry and premiums in the exchanges' first year. Small, rural counties that were bundled into a region with a larger urban neighbor attracted more insurers and saw lower benchmark premiums, but regions that mix very high and very low urbanity were less attractive to insurers, so there is a trade-off in drawing region boundaries too widely.

Read the full policy brief here.