This is a link to a study done by the Criminal Justice dept. They found only a 13.1 recidivism rate for a new crime committed, not necessarily a sex crime. When the data was restricted to a new sexual offense, the recidivism rates are even less. Also, this study includes only those offenders who were on probation, so that needs to be considered, as those who have been incarcerated and are not on paper were not included in the study. That would, no doubt, account for an even lower recidivism rate.
A rather lengthy study, but if one is interested in actually learning about the topic, it is worth the read.