What is the prevalence of female sexual offending? This is a question that is often asked but can never truly be known. This question is very complex and must take into account a number of variables. Due to a lack of standardization in reporting,combined with inconsistencies in research methods and overall definitions of sexual abuse, trying to obtain an accurate number is extremely difficult.
Jacqui Saradjian in her chapter of the book titled Female Sexual Offenders states:
The sexual abuse of a child always takes place in secret; therefore the true prevalence of any form of sexual abuse of children will always be secret. The more unthinkable, and consequently stigmatizing, the form of abuse, the greater the likelihood that it will be under-reported and, if reported, that it will not be recognized as abuse and therefore the secret will be kept. Sexual abuse of children, especially pre-pubertal children, instigated by women is still unthinkable in society today. Since information about the sexual abuse of children has been brought into the public domain, professionals have reported that both men and women are involved. Yet because the social construction of women has been such that this behavior remains ‘unthinkable’, that knowledge is dismissed. Consequently, each time it is ‘discovered’, it is again greeted with surprise followed by collective cognitive distortions relating to that knowledge, ensuring that the secret is kept.
Estimates can vary quite a bit depending on a number of variables. There are few who doubt that this type of sexual abuse is under-reported. So what about official crime reports? Here are two:
The United States Department of Justice found a rate of 8.3% for “Other sexual offenses” for females.
The Australia Bureau of Statistics found a rate of 7.9% for “Sexual assault and related offences” for females.
ATSA (The Association for the Treatment of Sexual Abusers) states:
It is estimated that less than 10% of all sex crimes result in a criminal conviction.
Sexual assault is one of the most under reported crimes, with 60% still being left unreported.
Males are the least likely to report a sexual assault, though they make up about 10% of all victims.
Various other studies have reported varying rates depending on the offense and time frame. For example these studies:
One in six adult men reported being sexually molested as children, and — in a surprise finding — nearly 40 percent of the perpetrators were female, a new study found. (Source Link)
In cases of daycare molestation, more than 60% of children who were molested, were molested by women. – (Source link)
Approximately 95% of all youth reporting staff sexual misconduct said they had been victimized by female staff. In 2008, 42% of staff in state juvenile facilities were female. (Bureau of Justice Report)
In a study of 17,337 survivors of childhood sexual abuse, 23% had a female-only perpetrator and 22% had both male and female perpetrators. ( Dube, Shanta R et al. “Long-Term Consequences of Childhood Sexual Abuse by Gender of Victim.” American Journal of Preventive Medicine. (2005):28(5), p 430 – 438.
According to a major 2004 study commissioned by the U.S. Department of Education – In studies that ask students about offenders, sex differences are less than in adult reports. The 2000 AAUW data indicate that 57.2 percent of all students report a male offender and 42.4 percent a female offender with the Cameron et al. study reporting nearly identical proportions as the 2000 AAUW data (57 percent male offenders vs. 43 percent female offenders).. (Source .PDF Download)
So what is the rate? We do not know. What we do know is that until it hits zero it is too high. My estimate would be about 16-20% if all cases were known. With the official crime reports rate being 8% and taking into account the under-reporting that occurs, especially with female perpetrated sexual abuse, I think that 20% is a conservative estimate.
 United States Department of Justice. (2003). Crime in the United States 2002, Federal Bureau of Investigation. Washington, DC: USGPO
 Australian Bureau of Statistics. (2005). Criminal courts, Australia, 2003-2004. (No. 4513.0). Canberra, Australian Capital Territory