Which figure triggers a NYC primary run-off?

No telling which figure triggers a run-off primary for the Democratic candidates.

No telling from wikipedia, New York City official election office sites or any other sites, as to which figure will trigger a run-off.

Here is an August 26, 2009 Quinnipiac University report on polls as to who is ahead in the city-wide races (mayor, public advocate and comptroller). The latter two races are for open seats.