By Stephen Fisher, 3^rd November 2026

Today the USA is holding its midterm elections. The poll-based forecasters and prediction markets are near certain that the Democrats will win control of the House of Representatives and they favour the Democrats for control of the Senate. Those predictions are directly or indirectly informed by opinion polls and historical experience, including the errors of opinion polls in previous elections. Election results can often end up being judged in light of expectations set by forecasts. That can get particularly complicated if the polls are systematically out, leading some to complain that the polls got it wrong while others claim that a party underperformed.

This blog post sets some of the poll-based forecasts for today’s elections in an historical context, using simple metrics, and thereby considers how the results might best be interpreted if the expectations of Democrat success are met, or not.