"I have no idea if that's an accurate number or not. I just don't know," he said.
The report was announced by a group that included Archbishop Timothy Dolan. Bloomberg aides took a more nuanced view of the figure, according to this New York Times story.
[C]ity health officials and groups that support access to abortion say that behind the 41 percent statistic — nearly twice the national rate — are complex social and legal factors: fewer obstacles to abortion in state law; the absence of mandatory sex education in New York City public schools; the ignorance of people, especially young ones, about where to get affordable birth control; and the ambivalence of young women living in poverty and in unstable relationships about when and whether to have children.
UPDATE: About that methodology. The study says their findings hold up, even when calculated by the method used by the Guttmacher Institute, a reproductive rights organization. A spokesperson for the Guttmacher Institute told me they too come up with a 41% abortion rate for NYC.