How AP calls a race at poll close

Using election research to call a race at poll close starts with what our AP VoteCast survey of voters says about which candidate will come out on top and by how much. For AP to consider calling a race before any results are released, the survey needs to show the winning candidate ahead by a margin that far exceeds the survey’s margin of error. But that number is just the start of the analysis that potentially leads to a “poll close call.” We’re also looking at what AP VoteCast says about who those voters are (such as their age, race and ideology) and in what part of a state they live. We want to know if a candidate is winning among all demographic groups and in all parts of a state. On the other hand, if the data suggests that relatively small changes in vote choice or turnout among a few groups could alter the outcome, we’ll wait and rely on the vote count to make the call.

We also closely consider when people voted. As more and more Americans vote before Election Day, that’s often the most important data point to consider when making a poll close call. Unlike an exit poll, AP VoteCast isn’t based on in-person interviews conducted on election days; rather, it’s a survey designed to capture opinions regardless of how and when voters choose to cast their ballot. Among the ways we do that is by interviewing some survey participants twice -- to confirm their vote choice or learn that they’ve changed their minds. Let’s use California as an example of how that approach tells us what we need to know to call a race as soon as polls are closed. AP VoteCast found that roughly two-thirds of voters in California didn’t cast a ballot in person on Tuesday; rather, they voted by absentee ballot. That means millions of voters — who backed Sanders by a wide margin and didn’t take part in the exit poll — had already put their ballots in the mail when Pete Buttigieg and Amy Klobuchar dropped out the race. What about those Buttigieg and Klobuchar supporters in California who did have time to consider a new candidate? AP VoteCast’s second round of interviews with those voters in states nationwide showed they were moving en masse to vote instead for Joe Biden. But in California, Sanders still had a significant edge over the former vice president, even among those who did not vote early. There was little sign the late developments significantly eroded Sanders’ margin. On AP’s Decision Desk, after examining the AP VoteCast data in detail, we concluded Sanders was winning California among voters who cast early ballots and among voters who cast their ballots on Tuesday. And there was not enough of a shift to Biden following Buttigieg and Klobuchar’s departures from the race to make up those gaps. At soon as polls closed, the APNewsAlert was on the wire: WASHINGTON (AP) — Bernie Sanders wins Democratic presidential primary in California, claiming biggest prize on Super Tuesday. The votes counted on Tuesday and in the days since have confirmed what AP VoteCast showed. We’ll be watching for the same trends on Tuesday in the AP VoteCast surveys of Michigan, Missouri and Mississippi, in search of the data we need to call the winner in each state.