What has come to be termed as "the low base rate problem" has traditionally plagued sex offender recidivism studies (Quinsey, 1980). As noted previously, lack of reporting, or underreporting, is higher in crimes of sexual violence than general criminal violence and may contribute to the low base rate problem. The following studies have found low base rates for sex offender populations:
Hanson and Bussiere (1998) reported an overall recidivism rate of 13 percent.
Grumfeld and Noreik (1986) found a 10 percent recidivism rate for rapists.
Gibbens, Soothill, and Way (1978) reported a 4 percent recidivism rate for incest offenders.
Samples of sex offenders used in some studies may have higher base rates of reoffense than other studies. Quinsey (1984) found this to be the case in his summary of sex offender recidivism studies, as have many other authors who have attempted to synthesize this research. There is wide variation in results, in both the amount of measured recidivism and the factors associated with these outcomes. To a large degree, differences can be explained by variations in the sample of sex offenders involved in the studies. Although this is a simple and somewhat obvious point, this basic fact is "responsible for the disagreements and much of the confusion in the literature" on the recidivism of sex offenders (Quinsey, 1984).
Furthermore, results from some studies indicate that there may be higher base rates among certain categories of sex offenders (Quinsey, Laumiere, Rice, and Harris, 1995; Quinsey, Rice, and Harris, 1995). For example, in their follow-up study of sex offenders released from a psychiatric facility, Quinsey, Rice, and Harris (1995) found that rapists had a considerably higher rate of rearrest/reconviction than did child molesters.
Conversely, Prentky, Lee, Knight, and Cerce (1997) found that over a 25-year period, child molesters had higher rates of reoffense than rapists. In this study, recidivism was operationalized as a failure rate and calculated as the proportion of individuals who were rearrested using survival analysis (which takes into account the amount of time each offender has been at risk in the community). Results show that over longer periods of time, child molesters have a higher failure rate—thus, a higher rate of rearrest—than rapists (52 percent versus 39 percent over 25 years).