A. W. Richard Sipe, a researcher, psychotherapist and former priest who spent his life studying the roots of sex abuse within the Roman Catholic Church, becoming one of the subject’s leading experts, died on Wednesday in the La Jolla neighborhood of San Diego. He was 85.

His wife, Marianne Benkert Sipe, said the cause was multiple organ failure.

Mr. Sipe’s research into celibacy and sexuality within the clergy helped establish a foundation for those studying, investigating and responding to the sexual abuse crisis of the 2000s. Along with describing how celibacy was lived, his work resulted in several striking estimates arrived at in the 1980s.

One was that fully 6 percent of all priests were sexual abusers of children and minors. Another was that at any given time, only 50 percent of priests were celibate — an estimate that the church said was overblown.

But Mr. Sipe’s most far-reaching conclusion was that those two phenomena were linked. Failures of celibacy among church leaders, he argued, even if they happened with adults, created a system of hypocrisy and secrecy in which the abuse of minors could take place.