Thursday, May 14, 2009

The Misuse of Statistics by Parents for Megan's Law

I've been exploring Parents for Megan's Law's web site. It actually has some pretty good material with which I agree, like their tips on prevention.

Parents for Megan's Law actually gives some helpful statistics which make it clear that most children are victimized by family members and acquaintances, not by strangers. Unfortunately, they do not point out that 95% of those arrested for sex crimes in New York State (their base of operations) are first time offenders and thus are not listed on any registry. They also do not point out that the vast majority of sex offenders in New York State are not arrested for a repeat offense.

Unfortunately, they also do their share of twisting and misusing statistics:

Their offender statistics page states: "The typical pedophile commits an average of 280 sexual crimes during his lifetime." The source given is Able, G., et al. Self-reported Sex Crimes of Nonincarcerated Paraphiliacs. Journal of Interpersonal Violence 2:3-25, 1987

You can find the quoted number (actually 281.7) on p. 16 of the study. Parents for Megan's Law states that the number applies to a "typical pedophile." Apparently, they think the typical pedophile does not target girls. The number quoted refers only to offenders with male nonincest victims. Actually, the majority of pedophiles in the study targeted girls and committed an average of 23.2 offenses (far fewer than those who targeted male victims). If you define the "typical pedophile" as someone who was diagnosed as being a pedophile (not everyone who has molested a child is a pedophile) who targeted both male and female nonincest victims, the accurate statement would be that the offenders committed an average of 128 offenses (less than half the number Parents for Megan's Law reports).

But wait, there is even more! The numbers above give the "mean" (average) number of offenses. The study also lists the "median" number of offenses. It is important to know the difference between "mean" and "median." Mean is the average number of offenses per offender. Median gives the halfway point---half the offenders have committed more or less than this number of offenses.

In the Abel study, the offenders with male nonincest victims committed an average of 281.7 offenses. The median number of offenses was 10.1. This means that half of the offenders committed less than 10.1 offenses. The median number of offenses for those with female nonincest victims was 1.4. This means that a small percentage of offenders in the study are responsible for a disproportionately large amount of the offenses.

If you included all pedophiles with nonincest victims, an accurate statement would be that half of the pedophiles in the Abel study committed 4 or fewer offenses and had 3 or fewer victims. This is a far cry from Parents for Megan's Law's claim: "The typical pedophile commits an average of 280 sexual crimes during his lifetime."

This is just some of the "fun" some can have with the numbers. The study has other problems as well.

The sexual abuse of children is a serious issue. One does not need to hype the numbers in order to raise hysteria.