How many religious youth become secular?

Tzohar, a (usually) wonderful group that does much to advance religious-secular relations in Israel, held its annual conference recently - and for once focused on issues affecting the religious community. One of the topics that came up was how Orthodox parents deal with children who leave the path of religion.

In the course of Ha'aretz's piece on the conference, reporter Yair Sheleg comes up with this astonishing claim:

Prof. Shraga Fischerman of Orot Israel College in the West Bank settlement of Elkana, who chaired the session on children who leave religion, said that about 25 percent of religious Zionist youths "defect" to secular lifestyles.

This seems to be extremely high - especially compared to the diaspora. A book I recently read - and reviewed here for The Forward - on the effects of taking a gap year in yeshivah in Israel included a throw-away line from Chaim Waxman, professor emeritus of sociology and Jewish studies at Rutgers University, who claims that, “According to estimates… more than 10 percent of the participants [in the Year in Israel program] leave Orthodoxy within five years of returning home.”