In the LA Times poll, Donald Trump has been consistently in the lead for the past month, even as other polls show Hillary Clinton ahead. Today, 27 days before November 8, doomsday has finally been postponed:
There is a 19-year-old black man in Illinois who has no idea of the role he is playing in this election. He is sure he is going to vote for Donald J. Trump….He’s a panelist on the U.S.C. Dornsife/Los Angeles Times Daybreak poll, which has emerged as the biggest polling outlier of the presidential campaign. Despite falling behind by double digits in some national surveys, Mr. Trump has generally led in the U.S.C./LAT poll.
….Our Trump-supporting friend in Illinois is a surprisingly big part of the reason. In some polls, he’s weighted as much as 30 times more than the average respondent, and as much as 300 times more than the least-weighted respondent. Alone, he has been enough to put Mr. Trump in double digits of support among black voters.
….He is also the reason Mrs. Clinton took the lead in the U.S.C./LAT poll for the first time in a month on Wednesday. The poll includes only the last seven days of respondents, and he hasn’t taken the poll since Oct. 4. Mrs. Clinton surged once he was out of the sample for the first time in several weeks.
In some way, I suppose it was worth experimenting with the unusual, panel-based design of the LA Times poll. However, their decision to weight lots of tiny subgroups separately is harder to defend. It’s the reason that one guy in Illinois can have a significant effect on the entire poll.
Nate Cohn’s piece on the LA Times poll is worth a read. It’s a very good introduction to the whole issue of poll weighting and how it works. There’s as much art as science to this stuff sometimes.