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The center uses a number of data lists and a complex identity-matching algorithm to identify whether records are up to date.

But it’s up to states to decide who gets culled. That can take time as officials try to make sure they aren’t canceling a valid voter.

In the District, election officials said they look at those who haven’t voted in two consecutive federal election cycles, and then send out canvas cards. Voters who appear to have moved are then put on the inactive list and ultimately are purged altogether.

Ms. Perez said interstate agreements can help with voter roll maintenance, but they also can flag names that shouldn’t be purged.

A Brennan Center report last year on Virginia voters said 40,000 names were purged based on information from an interstate agreement on voter rolls. But the report argued that there were “large error rates” in the purge, which led to some valid voters being eliminated from lists.

Some of those ended up having to cast provisional ballots on Election Day.