http://fivethirtyeight.com/features/election-update-leave-the-la-times-poll-alone/
I’m tired of hearing about the USC Dornsife/Los Angeles Times
tracking poll.
I’m tired of hearing about the poll from Donald Trump fans such as
Reince Priebus,
Matt Drudge and
Donald Trump himself.
1There’s nothing wrong with being your own No. 1 fan! They frequently cherry-pick that poll because it consistently shows much better results for Trump than the other surveys. As of Tuesday morning, for example, the poll showed the race as virtually tied — Hillary Clinton 44.2 percent, Trump 44.0 percent — even when the
national poll average has Clinton up by about 6 percentage points instead.
This has been a fairly consistent difference between this poll and most others. Take the LA Times poll, add 6 points to Clinton, and you usually wind up with something close to the FiveThirtyEight or
RealClearPolitics national polling average. What’s the source of the LA Times poll’s Trump lean? There are good “explainers” from
The New York Times’s Nate Cohn and
Huffington Post Pollster’s David Rothschild. Long story short: The poll’s results are weighted based on how people said they voted in 2012. That’s probably a mistake, because people often misstate or misremember their vote from previous elections.
2In particular, it’s likely that more people say they voted for the winner than actually did. Imagine, for example, that respondents in a poll claim they voted for Barack Obama by 10 percentage points, when he actually beat Mitt Romney by 4 percentage points. The LA Times poll will conclude that it has too many Obama voters, most of whom are also Clinton voters, and therefore downweight Clinton’s numbers. But some of those Obama “voters” actually voted for Romney or sat the election out.
The poll does some other things differently also, some of which I like. For instance, it allows people to assign themselves a probability of voting for either candidate instead of saying they’re 100 percent sure. And the poll surveys the same panel of roughly 3,000 people over and over instead of recruiting new respondents. That creates a more stable baseline and can therefore be a good way to detect trends in voter preferences, although it also means that if the panel happened to be more Trump-leaning or Clinton-leaning than the population as a whole, you’d be stuck with it for the rest of the year.