Researchers commissioned by US Roman Catholic bishops to analyse the pattern of clergy sex abuse over decades have concluded that homosexuality, celibacy and an all-male priesthood did not cause the scandal.
The report from the John Jay College of Criminal Justice in New York said about 44% of the known abuse cases involved priests who were ordained in the 1940s and 1950s, at a time when seminaries did not properly train them to live a celibate life.
These men were not equipped to withstand the social upheaval of the 1960s, which was a time of an increase in sexual activity and a spike in crime in society at large, the authors said.
The full report is the last of three studies commissioned by the US Conference of Catholic Bishops as part of child protection reforms adopted in 2002 at the height of the American abuse crisis.
Dioceses nationwide have received allegations from more than 15,700 people against about 6,000 clerics since 1950, according to reports John Jay and others compiled for the bishops. The findings are scheduled to be released today.
The debate over what caused the crisis has fallen along ideological lines, with liberals blaming mandatory celibacy or the lack of women in positions of authority.
Conservatives pointed to gay priests, since the overwhelming majority of known victims were boys.
The John Jay researchers, however, said that the offenders chose boys mainly because the clergy had greater access to them.
According to the researchers, abuse cases peaked in the 1970s, then began declining sharply in 1985, following a similar trajectory for the rate of abuse in society at large.
The bishops hoped the results of the study, which were first reported by Religion News Service, would help them better identify potential offenders.
The researchers, however, said they found no "psychological characteristics" or "developmental histories" that distinguished guilty priests from clergy who did not molest children.
"No single 'cause' of sexual abuse of minors by Catholic priests is identified as a result of our research," the authors wrote.
Although the victims studied by the researchers were all legally minors, the authors said only a tiny percentage of accused priests - less than 5% - could be technically defined as paedophiles.
The John Jay researchers define paedophile as an adult with an intense sexual attraction to prepubescent children.
However, victim advocates have disputed that classification, since boys aged 10-14 were the largest group of known victims, which could include children who had not yet gone through adolescence.
Critics argue the study cannot be trusted since the raw data was provided by the bishops.
The Survivors Network of Those Abused by Priests said the study is useless for protecting children because the focus is on priests, not bishops. No bishops have been disciplined by the pope for keeping offenders in ministry without warning parents or police.
Sister Mary Ann Walsh, a spokeswoman for the bishops' conference, said the bishops fully co-operated with the $1.8m (€1.26m) study, which was funded by the bishops, foundations and a grant from the US Department of Justice.
"John Jay was chosen to do the study because of its independence from the church," Sister Mary Ann said.
"John Jay was free to consult whomever they wanted and they did so."