Pollsters

60 firms shown · 9317 polls · 54% verified against a primary source

A lean is the firm's average deviation from what other firms said about the same race within 14 days, over every race it has polled. It is never measured against an election result. Firms with fewer than 4 such comparisons get no number. The rest are shrunk toward zero by a weight of 5.0, so a firm seen five times is pulled halfway and one seen fifty barely moves.

This measurement cannot see an error the whole industry shares: if every firm is wrong in the same direction, every firm's deviation from the others is still zero. That error is estimated separately, from results, as the correlated polling-error term, and the two are never added together.