For those of you not into adolescent pop culture of the 1970s, today’s title is explained at the bottom.

Updated to reflect new polls. The bounce is smaller than the original estimate.

We have five polls that measure a post-convention bounce for Presidential candidate Donald Trump (R):

NBC/SurveyMonkey: steady at Clinton-Trump 46%-45% (July 11-17 to July 18-24).

CBS: an increase from Clinton-Trump 40%-40% (July 8-12) to 43%-44% (July 22-24), a 1-point swing from a tie to Trump +1%.

YouGov: A 1-percentage-point change from 40%-37% (July 15-17) to 40%-38% (July 23-24).

Morning Consult shows a 6-point swing from 41%-39% (July 14-16) to 40%-44% (July 22-24).

CNN shows a shift from Clinton-Trump 49%-42% (July 13-16) to 45%-48% (July 22-24), a 10-point swing from Clinton +7% to Trump +3%.

The measure of the post-RNC bounce so far is a median swing of 4 percentage points 1 percentage point. For stragglers, see HuffPollster.

One point is not an impressive change. Recall that in states won by Mitt Romney (R) in 2012, Trump has been lagging by about 9 percentage points. A CBS crosstab (can’t find at the moment – perhaps a reader can help) reports that Trump’s progress was made entirely with Republicans – whose support went up by 2 points. This suggests that with many reluctant Republican voters, Trump did not close the sale. Also, note that some of the change may be changes in how likely people were to respond to the survey. And of course, it remains to be seen whether any increase in support is lasting.

Current numbers do indicate that the race has closed up a bit. As of today, the election could possibly go to Trump. However, the election is not today.

Convention bounces aren’t what they used to be. Shown below are patterns that come from Gallup data, 1984-2012 in the net change in direct support for a candidate.



As you can see, the median change in candidate support in modern times is only 2 or 3 percentage points.

This reflects what I wrote about over the weekend, decreases in net impact, i.e. change in “likelihood of supporting candidate”, which allows favorability to be measured without forcing voters to change their minds:



In the CNN/ORC poll (see Q13), 42% of respondents said they were “more likely to support Trump,” and 44% said “less likely.” That’s a net difference of negative 2 percent, which is worse than any value in the graph above. By that measure, the Republican convention was a failure.

In both graphs, a notable shift occurred around the time that national elections became more polarized, in 2000. We are in an era of government shutdowns, endless Congressional investigative hearings, criminalization of political opposition, and ever-more-contentious judicial nominations. Voter entrenchment appears to be just one more symptom.

In the coming week you may be surprised to see relatively little change in the Princeton Election Consortium electoral-vote tracker and November win probability. There are two reasons: (1) We use state polls, which take time to reflect national shifts. (2) The Bayesian-win probability listed in the banner uses polls over the entire 2016 campaign to set a prior expectation for where things are likely to head. The second assumption also has the more traditional name of “regression to the mean.” Effectively, these two mechanisms prevent the calculations from spinning out of countrol whenever there is a momentary bump in polling. Therefore, today’s November win probability is 80%.

Of course, if the race shifts in a lasting manner, it will show up eventually. Just to state the obvious, now is not the optimal time to gauge where the race is headed in steady state. Recall that in 2008, the Republican convention and the addition of Sarah Palin to the ticket led the race to briefly appear tied.

If you want to see the prediction without the Bayesian prior, the assumption that polls can drift equally in either direction, toward Clinton or toward Trump, is the random drift probability. Today, that probability is 65%.

Which brings us back to the title of the post, which is adapted from a lyric by AC/DC. It’s my belief that one big poll should be held every night:

P.S. A reader, Dmitriy, wants to know if this is a normal swing in the course of past elections. In terms of state polls, we don’t know yet. I would guess that once we have enough data, the answer will be yes.

Here is a view of the last three rollercoasters (click to enlarge):

