Post-convention polling bounce for Hillary Clinton

Last week an outlier CNN poll claimed Donald Trump had a “big bounce” after his apocalyptic convention in Cleveland. Donald Trump bounces into the lead. The short-fingered vulgarian trumpeted this poll to claim that he had a yuuuge post-convention bounce.
According to Nate Silver at Five Thirty Eight, Trump’s polling average bounce after the GOP convention was 3 to four percentage points. According to Sam Wang at the Princeton Election Consortium, Trump’s polling average bounce after the GOP convention was only one point (see below).

Now that the post-convention polls for the Democratic convention are being released, the short-fingered vulgarian has something else for which he needs to compensate for his inadequacy.

The CNN poll released today claims Hillary Clinton has a 7 point post-convention bounce. Post-convention poll: Clinton retakes lead over Trump:

Hillary Clinton emerges from her party’s convention in Philadelphia with a restored lead over Donald Trump, having earned a 7-point convention bounce, according to a new CNN/ORC Poll.

In a two-way head-to-head matchup, Clinton tops Trump 52% to 43%, and in a four-way matchup including third party candidates Gary Johnson and Jill Stein, Clinton leads 45% to 37% with Johnson at 9% and Stein at 5%.

Nate Silver reports that Election Update: Clinton’s Bounce Appears Bigger Than Trump’s:

Initial polls conducted after the Democratic National Convention suggest that Hillary Clinton has received a convention bounce. In fact, it appears likely that Clinton’s bounce will exceed Donald Trump’s, which measured at 3 to 4 percentage points. Thus, Clinton will potentially exit the conventions in a stronger position than she entered them, perhaps also making up for some of the ground she lost to Trump earlier in July.

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[W]hen evaluating the gains a candidate has made, it’s important to note when the previous poll was conducted. Based on our models, Clinton led by 6 to 7 percentage points throughout most of June, but her lead dissipated to around 3 percentage points by mid- to late July, just before the conventions. Then, after the Republican National Convention in Cleveland, Trump pulled into an approximate tie with Clinton. It’s those post-RNC polls that make for the best comparison when describing Clinton’s bounce.

So far, however, the post-convention polls have been strong enough for Clinton that there isn’t a lot of need to worry about semantics. They suggest that she possibly holds a lead over Trump in the mid- to high single digits, instead of being tied with him. Here are the fully post-convention polls we’ve seen so far:

• A CBS News poll has Clinton ahead by 5 percentage points, in the version of the poll that includes third-party candidates (which is the version FiveThirtyEight uses). Trump led Clinton by 1 point in a CBS News poll conducted just after the RNC, so that would count as a 6-point bounce for Clinton.
• A Morning Consult poll also showed Clinton up by 5 percentage points, representing a 9-point swing toward her from a poll they conducted last week after the RNC.
• A RABA Research national poll, conducted on Friday after the convention, has Clinton with a 15-point lead. RABA Research’s national poll has been something of a pro-Clinton outlier. Still, the trend in the poll is favorable for Clinton. She’d led Trump by 5 percentage points in RABA Research’s poll just after the RNC, meaning that she got a 10-point bounce.
• Finally, a Public Policy Polling survey has Clinton up by 5 percentage points. Because PPP did not conduct a post-RNC poll, we can’t directly measure Clinton’s bounce. But their previous national poll, in late June, showed Clinton up by 4 percentage points. Therefore, their data tends to confirm our notion that the conventions may have reset the race to approximately where it was in June, which was a strong month of polling for Clinton.

Sam Wang at the Princeton Election Consortium reports, Post-Democratic convention bounce:

So far, four five pollsters have released national surveys using samples taken after the end of the Democratic National Convention, and have data from the post-RNC period. The median swing is a 7.0 ± 1.1 2.0 % (± estimated SEM) move toward Hillary Clinton.

The Pre-DNC measurement from PPP was taken in June, predating both conventions. The resulting swing therefore represents a combination of the Republican and Democratic conventions. However, since the median post-Republican convention swing was only 1 point, it was still informative and I included it. Since you can do medians in your head, you can see that this does not make a difference given the current data set.

I have seen some sniffy comments in the news that Hillary Clinton’s post-convention bounce is smaller than Bill Clinton’s bounce in 1992. However, by current standards, Hillary Clinton’s bounce is large. As I wrote the other day, post-convention bounces have been small for presidential elections since 1996, which I suggest is a symptom of political polarization: voters get entrenched in their support.

Donald Trump, like George Costanza, is suffering from “shrinkage.” “I was in the pool! I was in the pool!”