Aftermath: Election results and interactive maps can be found at the NYT. DeBlasio currently has 40.3%, so a mayoral runoff appears to be avoided, as I predicted. Stringer wins comptroller – I was on the wrong side of that. However, as I’ve said before, with my methods, anything in the 20-80% probability range is a knife-edge situation. The comptroller race was such an example.

In today’s New York City Democratic primary, front-runner (and progressive) Bill DeBlasio has drawn 41.9+/-1.3% of decided voters (n=5 polls since late August). The threshold for avoiding a runoff is 40%, and if (and that’s an if!) polls are any indication, he will reach this threshold with a 90% probability. Note that primaries are harder than usual to predict since voters can be volatile.

Speaking of volatile: who does DeBlasio have to thank for this turn of events? To a large extent Anthony Weiner, for imploding. Examining changes over the last 10 polls, it seems that about 45% of disaffected Weiner voters went to DeBlasio. DeBlasio seems to be the leading choice for a wide variety of NYC voters, since undecideds seem to have split in the same proportions.

This means it would have been in the other candidates’ interest to prop up Weiner, especially second-place candidate Bill Thompson (21.7 +/-0.2%) or third-place Christine Quinn (19.4 +/- 0.7%), who may not get a face-off with DeBlasio. Then again, Weiner’s negatives are quite high, so such a move might have backfired.

In the other high-visibility primary, for comptroller, Manhattan borough president Scott Stringer has largely closed the gap with former governor Eliot Spitzer. However, Spitzer still leads by 2.0 +/- 1.7% (n=3 September polls). That puts Spitzer’s win probability at 80%, in knife-edge territory.

Update. From a conversation with Mark Blumenthal: