Polymarket runs several markets on who will control Congress after Tuesday's US midterms. They are separate order books with separate traders: one for the House, one for the Senate, and one "balance of power" market that prices the four combinations.

That makes a nice consistency test. If the combination market says "Democrats win both" and "Republicans win the Senate, Democrats win the House", then adding those two should give you roughly what the House market says on its own.

So we checked, on the morning of 2 November (prices as read at 01:18 UTC).

What each market priced

Market Outcome Price

House Democrats control 94.5%

Senate Democrats control 71.5%

Balance of power Democrats win both 70.5%

Balance of power Republican Senate, Democratic House 23.5%

Balance of power Republicans win both 5.5%

Balance of power Democratic Senate, Republican House 0.5%

Rebuild the House and Senate from the combinations

House, Democrats = "both" 70.5 + "R Senate, D House" 23.5 = 94.0% .…