Don’t Get Excited About Polling Numbers For A Couple Of Weeks

They could be unstable and change quickly following the Democratic convention.

As the Democratic National Convention begins on Monday, we’re going to start seeing results of polling conducted after the close of the Republican National Convention.

Don’t get caught up in those numbers. They could change very quickly.

Following the polls closely immediately after each convention is only good for one thing: Trying to gauge how much of a bump the candidate got. These polls don’t mean that the race, as a whole, has shifted substantially ― especially not before both conventions have taken place.

Conventions have often resulted in small to medium polling bumps for the candidate whose party just convened. The gatherings typically help unify the parties, particularly if there were divisive primaries ― which both Democrats and Republicans experienced this year. They also usually correspond to vice presidential candidate announcements, which might (or might not) help the candidate.

Even with the Republican Party’s somewhat unorthodox convention this year ― including some last-minute efforts to overthrow the presumptive nominee before the formal nomination vote ― Donald Trump could see some polling gains in the next few days.

But now the Democrats have the stage for a week. Hillary Clinton announced Sen. Tim Kaine (D-Va.) as her vice presidential pick on Friday night. The attention is turning to the other side, and within a few days it could be Clinton’s turn to get a convention bump in the polls.

Her bump isn’t guaranteed either, though. A new email scandal for the DNC that resulted in party chairwoman Debbie Wasserman-Schultz’s resignation means the Democratic convention starts on shaky ground. Granted, that’s not as big a deal as substantial numbers of Republican delegates revolting against their own nominee, but it’s not a great start. Democrats also need to bring the party back together after a tough primary season.

So there’s the possibility of a post-convention swing in Trump’s direction, in Clinton’s direction, both or neither. Any of those swings could be temporary or permanent. The instability in the polls will be reflected in poll-based presidential forecasts as well, such as those published by FiveThirtyEight, The Upshot and the Princeton Election Consortium.

FiveThirtyEight’s polls-only model has shifted more favorably in Trump’s direction in the last week ― he now has about a 40 percent probability of winning the presidency, according to that model ― but that movement was in progress before the convention. The other two poll-based models haven’t moved much over that time period but could as new polls come in.

If you want to accurately know the state of the presidential race, wait a couple of weeks until the convention furor has settled into the August campaign inferno.