Polling firms have an obligation to do good work, but measuring the “accuracy” of election polls is a more complicated notion than conversations about whether “the polls got it right” or whether “the polls can be trusted” allow. The complications are many: What’s the right way of measuring accuracy? How close to the final margin does a poll need to be to be considered accurate; is being within the poll’s margin of error close enough? What’s the lifespan of a polling estimate; how close to election day should a poll be conducted for it to count as a prediction?
At its most basic, reliable and accurate survey results come from a pollster’s ability to find a good list from which to draw a representative sample, their ability to encourage those sampled to participate, and their skill at asking fair questions that are understood in the same way by each participant. These technically challenging tasks are each within a pollster’s control.
What is beyond a pollster’s control, and what many people overlook when talking about poll accuracy, is the role of shifting voter attitudes. A question that asks how someone intends to vote is measuring a current belief and not an actual behavior. How wise is the assumption of stable voter attitudes when the major-party candidates are bombarding voters with messages? In the 2020 election, the presidential candidates spent nearly $100 million on advertising in Pennsylvania between July and November; is it reasonable to expect that campaign spending, media coverage, and the public conversations these encourage produce unchanging, immobile attitudes about turnout and preference?
This assumption is further strained in a state like Pennsylvania that is hotly contested and evenly divided. In Pennsylvania, only a small share of voters need to change their minds about turning out to vote or about who they intend to support to make a poll that was accurate when conducted look inaccurate on election day. There is ample evidence that attitudes about voting and about vote preference change throughout the course of the campaign, even if those preferences become a bit more stable in the closing weeks of a race.