Here is the report, in PDF format. The report examines the question as to whether the increase in clergy sex abuse cases is caused by the presence of gay men in the priesthood.
Ruth Report: “The share of homosexual men in the priesthood rose from twice that of the general population in the 1950s to eight times the general population in the 1980s. This trend was strongly correlated with increasing child sex abuse.”
This claim is problematic. It is difficult to estimate the percent of gay men in society as well as the percentage of gay priests in past decades, when homosexuality was disapproved by secular society. As society changed its views, more men were willing to be open about their sexual orientation, and more priests as well.
Wikipedia: “The percentage of people who are gay or lesbian and the proportion of people who are in same-sex romantic relationships or have had same-sex sexual experiences are difficult for researchers to estimate reliably for a variety of reasons….” [Homosexuality article]
The claim that there were 8 times as many gay men in the priesthood as in society is highly unlikely. Estimates of the percent of men who are gay is as high as 5 to 10%. Eight times that figure would be 40 to 80%. I know from being a life-long Catholic that the percent of priests who are gay is well below those figures.
Ruth Report: “By the 1980s homosexual men made up over 16% of the presbyterate, which is over 8 times that of the general population.”
The Report’s estimate of gay men in the general population is less than 2%. That figure is unrealistically low. It may be that less than 2% of the population of adult men were openly gay, but the Report assumes that figure is the total. Also, the estimate of gay priests is particularly difficult to assess, since the Church is opposed to homosexuality. But 16% is almost 1 in 6. I don’t think 1 in 6 priests that I’ve known in my life were gay. What do you think?
Correlation is not causation. The rise in the percentage of gay priests may be partly due to the ability, only just recently, for gay priests to come out, without losing their ministry. Even if there were an increase in gay priests, the implied claim that this is the cause of abuse is highly unlikely. Studies of child sexual abuse (CSA) in the general population have found that most abusers are not gay.  My own work with abused children confirms this. The typical abuser of boys are heterosexual adult males. The Ruth Institute Report assumes that a man who abuses boys is gay. That is widely-known to be false among persons who actually work with victims.
Ruth Report: “A quarter of priests ordained in the late 1960s report the existence of a homosexual subculture in their seminary, rising to over half of priests ordained in the 1980s. This trend was also strongly correlated with increasing child sex abuse.”
Again, correlation is not causation. The increase in gay priests could be caused by the influence of sinful secular society, which increasingly approves of homosexuality and of sexual sins more generally. The same influence could well have caused the increase in child sex abuse cases. And that explanation is a better fit for the information from CSA cases in the general population, where gay abusers are 1 to 3% of all abusers, and most abusers of boys are straight men.
But even this increase in cases is questionable, since it was more difficult for boys to disclose abuse by a priest in the 1950s, when priests and Catholicism had much influence in society. Priests were assumed to be holy and were above reproach. So it may well be false that the number of cases increased from the 50s to the 80s. Then the subsequent decrease in cases later on may be due, as the Report notes, to the fact that disclosures often occur decades after the abuse.
The Ruth Institute Report was not published in a peer-reviewed medical or psychiatric journal. The author, a married Roman Catholic priest, Fr. D. Paul Sullins, has published peer-reviewed studies before. Why is this study not also published in like manner? The study does not read like a medical study, to my eyes. I’ve read hundreds of medical studies for my book Healthy Eating versus Mortality and my forthcoming book on abortifacients. The Sullins study does not read like a real study. It notes a correlation and then draws an unwarranted conclusion from that correlation.
In all likelihood, the correlation is either due to bias in the way that the data is handled by the study author, or it is due to a similar causation. Sexual sins have increased in society since the 1950s, as a result, more gay men dare to apply to the priesthood and more are accepted; for the same reason, increase in sexual sins in society, there are more abusers.
Interestingly, Sullins does not state that most abusers identify as gay. Other researchers have found that the typical clergy member who abuses boys is heterosexual.
“Sex-offending clergy frequently report that they victimize boys (even if they report being heterosexual) because boys are a victim of convenience (Plante, 2004). They often report that they have ready access to and trust with boys rather than girls.” 
The effects of this bias study and its false conclusion could be very harmful to the Church. The study claims that the increase in gay clergy is the cause of the increase in abused children. The study even states: “12,594 children, most of them boys, who would have been saved from sexual victimization by Catholic priests.” That conclusion is absolutely not warranted by a mere correlation, especially when the typical abuser is heterosexual.
What will happen next? There may be a witch hunt to remove celibate gay priests from the priesthood, as if they were all abusers. And the actual abusers, who are generally heterosexual, will remain untouched. Then they will declare “mission accomplished”, while the abuse continues. That is the problem with this false conclusion that gay clergy are responsible for child abuse in the Church.
However, I must point out that all clergy who take vows of celibacy must refrain from all sexual activity. If a gay priest refuses to be celibate, he should be removed from the ministry. But he should not be treated as if he were a child abuser.
More Reading: No, homosexuality is not a risk factor for the sexual abuse of children by Thomas G. Plante, Ph.D.
Ronald L. Conte Jr.
 Jenny, Carole, Thomas A. Roesler, and Kimberly L. Poyer. “Are children at risk for sexual abuse by homosexuals?.” Pediatrics 94.1 (1994): 41-44.
 Thomas Plante, “Homosexual Applicants to the Priesthood: How Many and Are They Psychologically Healthy?” Pastoral Psychology 2007.