The paper quoted in the accepted answer cites its info to a book edited by Plante, which actually gives the info as
that more than 40 percent of Catholic priests are homosexual (Cozzens,
2000), and the vast majority of them do not abuse anyone, the request to
evaluate priests or priest applicants to diagnose homosexuality seems odd.
The ultimate reference behind this chain being
Cozzens, D. (2000). The changing face of the priesthood. Collegeville, MN:
which has an entire chapter (around p. 100) on the topic. In it we find that:
- an NBC report put the figure between 23% and 58% of Catholic clergy having a homosexual orientation
- "Sociologist James G. Wolf in his book Gay Priests concluded that 48.5% of priests and 55.1% of seminarians were gay"
- "I heard a religious order priest with long experience in both formation and leadership state publicly at a conference on AIDS and the mission of the Church that 80 percent of his large East Coast oder was gay."
The amount of original info is alas limited to that last quote and there's no direct citation for the NBC report... but rather to
Timothy Unsworth, The Last Priests in America, (NY: Crossroad, 1991) p. 248
In addition to the book edited by Plante, the paper quoted in the accepted answer cites a newspaper column by Plante in SF Gate... which alas gives no figures on prevalence of homosexuality among the clergy. So the paper cited in the accepted answer, despite being peer-reviewed, appears to have come up with that range of numbers by a somewhat strange indirect synthesis, not directly from the sources it cites.
Anyway, my best guess from all this is that Penn & Teller figures (20-50) are approximations to the numbers (23-58) from this NBC report... which I don't have first-hand knowledge of.