Democratic polling bias is mostly a presidential elections problem

Weighted-average statistical bias of polls in the final 21 days before presidential, Senate, House and gubernatorial general elections between 2015 and 2025

Note: Bias is calculated only for elections where the top two finishers were a Republican and Democrat. Therefore, it is not calculated for presidential primaries. The 21 day cutt-off is based on a poll's median field date. Averages are weighted by the square root of the number of polls that a particular pollster conducted for that particular type of election in that particular cycle. Polls that are banned by Silver Bulletin are excluded from the analysis.
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