The Republicans are gearing up for an elaborate national convention in pursuit of the coveted post- convention bump. However, research has shown that these jumps in the polls often have more to do with the situation surrounding the convention than the convention itself in that even the most robust post-convention boost doesn’t necessarily lead to winning in the election.
A post-convention bump is a gain in the polls by a candidate immediately after their party’s convention. The most prominent convention bump was Bill Clinton’s in 1982. On the other hand, John Kerry lost one point after the democratic convention in 2004. Due to these examples, some commentators view the bump as an indicator of whether or not the candidate will win the election, and these gains are eagerly sought.
Thomas Holbrook, a professor at the University of Wisconsin analyzed poll data from U.S. presidential elections since 1964 and concluded that these jumps in the polls do not necessarily indicate success in the elections, noting that a large bump may demonstrate that a candidate is doing worse than expected.
Holbrook’s data shows that a candidate who is behind where he was expected to be at the time of the convention often gets a large bump, while a candidate who is doing better than expected in the polls is likely to get a smaller one. For example, in 1964, Barry Goldwater got a 12-point bump after the convention; before the convention name is running 16 points behind in the polls.
It’s worth noting that, despite his boost, Goldwater didn’t win the election. Meanwhile, Johnson, was doing six points better than expected, got no bump. This variation between the candidates expected and actual performance has the largest impact on the post-convention bump. Frank Newport, the editor in chief of the Gallup polling organization noted that these gains often disappear within a few weeks.
Holbrook doesn’t speculate on why expectation plays such a strong role in determining the size of a host convention bump, but it’s possible that a convention PR offensive could, at least temporarily, call the candidate who is doing worse than expected because of a recent negative event. For a candidate who is already doing well, the PR blitz may have less effect.
Another factor that affects the size of these bumps is the timing of the convention. Holbrook’s data shows that the candidate (usually the challenger) who has the first convention is more likely to get the large boost in the polls, suggesting that the party to get its message out first as an advantage, at least temporarily. This effect is particularly strong when there’s a large gap of time between the two conventions.
While these factors of expectations and timing can be used to predict a bump fairly reliably, Holbrook and Newport emphasize that the events surrounding the convention can effect have the size of the point gain and how long it lasts. Observers believe that Clinton’s epic 16-point bump in 1992 was partly due to the withdrawal of independent Ross Perot a week earlier.
Events can also have a negative effect on a candidate’s performance in the polls. Holbrook cites the 1984 democratic convention, which was plagued by dissent and infighting and where the candidate who formed four points worse in the post-convention polls than the measures of expectation and timing would have predicted. Given this evidence, it would be interesting to see what the disruption of hurricane Isaac might do this year’s RNC Convention.
Hurricanes aside, both experts agree that the bombs this year are likely to be smaller than those seen in the past for two reasons: first because the conventions are back to back off, and second because they are happening late in the campaign.
Historically, conventions were held earlier in the summer when there would have been more undecided voters. Newport suggested that when conventions were held close together the parties’ messages could become confused, and so they would make a significant impact on the voters. Similarly, this late in the campaign so much has already been said about both of the candidates that the conventions may seem like just one more campaign ad.