The Kinsey group compiled data on penis size for the detailed report on sex offenders. Various classes of offenders were asked to estimate their penis length on the ventral surface from the abdomen to the tip of the penis.

Penis lengths for various groups were found to average 6.3 to 6.5 in. It was found that only one group -- "the aggressors v. minors" - reported an above-average length penis (around 6.75 in.). It was pointed out that contrary to expectation the estimated penis length of the exhibitionists was not unusual.

These efforts represent one of the few attempts to discover correlations between penis size and types of sex offender. Some writers have seen fit, however, to remark on the penile characteristics of offenders. For instance it has been pointed out, by Colin Wilson in his "Origins of the Sexual Impulse" that the penis of the sexual murderer DeWitt Clinton Cook was "so tiny that he and his wife were forced to satisfy one another orally."