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Why many polls need to weight on party affiliation or past vote

Pew Research Center · Scott Keeter and Courtney Kennedy · last updated
There are two big reasons why many pollsters now weight their surveys on political characteristics such as party affiliation or past vote, when this wasn’t common practice a decade ago: to correct for a systematic bias that emerged around 2016 and to protect against poll-to-poll volatility driven by who participates rather than real changes in […]