(SLATE) You sort of know there is a convention bounce that you should sort of ignore, but why? What’s actually in a polling bump? The recent Republican National Convention featured conflict and controversy and one very dark acceptance speech—enlivened by some D-list celebrities (welcome back Chachi!)—but it was still enough to give nominee Donald Trump a big, if temporary, boost in many polls. This swing, which occurs predictably in election after election, is typically attributed to the persuasive power of the convention, with displays of party unity persuading partisans to vote for their candidate and cross-party appeals coaxing over independents and voters of the other party.
Recent research, however, suggests that swings in the polls can often be attributed not to changes in voter intention but in changing patterns of survey nonresponse: What seems like a big change in public opinion turns out to be little more than changes in the inclinations of Democrats and Republicans to respond to polls. We learned this from a study we performed during the 2012 election campaign using surveys conducted on the Microsoft Xbox. This was a highly nonrepresentative sample—much younger and more male than the voting population—but we were able to use statistical methods to create a daily voter intention poll that proved extremely accurate. The advantages of the survey were 1) people were allowed to respond multiple times, on different days, and thus we were able to track changes in individuals’ attitudes, and 2) the sample was large enough, over 15,000 per day on average, that we could get day-by-day estimates of voter intention.