This question resolves Yes to the first year, and all subsequent years, where one US state elects its entire slate of US Congress representatives using some kind of proportional representation system.

The state must have at least 2 total representatives, and all voters in the state must vote on the same ballot for Congress. Instead of electing one representative per congressional district, all representatives in the state should be elected on a statewide basis for that year to resolve Yes.

If there are elections handled with a proportional method at a level smaller than a full state, that will not count for this market -- at least one state's representatives need to be handled completely by one proportional election. (If some state has a lot of representatives but splits them up into 3 or 5 geographic bundles, that will not count, but if you are interested in that, it sounds like you can make a new market!)

If multiple states combine their representative elections into a single coordinated election, this market can resolve Yes based on whether everyone in one single state was voting in the 'same' election.

Resolves Yes in the first year this happens -- the year of the election, not the year they are seated in Congress. All subsequent years also resolve Yes. All years that pass without a state meeting this criteria resolve No.

If some year(s) look more likely or have more interest, we can add those years in between the existing options.

Please ask questions below and assist me with 'fixing' the criteria, because I definitely need help with it. I don't want this to be a 'gotcha' moment -- I want to know when a state will actually use a proportional method to elect representatives instead of winner takes all within each district. Consider the criteria as potentially fluid for the time being, and as smarter commenters than me roll in, they can be updated.