Buoyed by a Supreme Court ruling, opponents of gerrymandering want to get more state legislatures out of the business of drawing congressional districts. So it’s worth examining the performance of the independent redistricting commissions validated by the court on Monday.

Arizona, via a ballot initiative in 2000, was one of the first states to entrust congressional boundaries to an independent commission, and California followed suit in 2010. Four other states have their congressional districts drawn by independent panels in an effort to make the process less partisan and yield more competitive districts. But those commissions were formed by their respective state legislatures and were not affected by Monday’s ruling.

Measuring the success of an independent commission is tricky, as it’s impossible to know how a legislature’s lines will have differed from a commission’s in the same year. And other factors like people’s relocations can alter a district’s ideological balance. But the evidence suggests that the commissions yielded more competitive races in Arizona and California.