Last year we did an N=1 poll on the Democratic primary election for governor of New York. And the poll worked pretty well. To recap:

A survey with N=1! And not even a random sample. How could we possibly learn anything useful from that? We have a few things in our favor:

– Auxiliary information on the survey respondent. We have some sense of our respondent’s left-right ideology, relative to the general primary electorate.

– An informative measure of the respondent’s attitude. He didn’t just answer a yes/no question about his vote intention; he told me that he wasn’t even considering voting for the alternative candidate.

– A model of opinions and voting: Uniform partisan swing. We assume that, from election to election, voters move only a small random amount on the left-right scale, relative to the other voters.

– Assumption of random sampling, conditional on auxiliary information: My friend is not a random sample of Democrats, but I’m implicitly considering him as representative of Democrats at his particular point in left-right ideology.

Substantive information + informative data + model + assumption. Put these together and you can learn a lot.

Today I ran into survey respondent and I thought I’d ask him, my representative center-left Democrat, who he supported in the presidential race. Not who he thought would win, but who he supported.

So I asked him, he paused for about a second, and then said, Beto.

**P.S.** According to Predictwise, Beto’s currently at 15%. I don’t really have a sense if this is too low or too high. And, in any case, there are several reasons why primaries are hard to predict. But, for now, given my N=1 poll, I’m going with Beto.

Predictwise also has odds for the Republican nomination. Their probabilities are Trump 86%, Kasich 20%, all else 4%. The Kasich number doesn’t seem right to me. Trump 86%, that seems reasonable enough, but conditional on Trump not being the nominee, is there really an 80% chance that it will be Kasich? That conditional probability seems too high. I guess that implies I should lay some money on Mike Pence, Paul Ryan, etc.