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Commentary on Pedersen and Skardhamar (2010): does cannabis use predict non-drug offending?

The paper by Pedersen & Skardhamar [1] is an excellent contribution to knowledge. They use data from the Young in Norway Longitudinal Study, which is an extremely important four-wave population survey. They show that cannabis use at ages 15 and 20 years predicts subsequent offending, but that the predictability is greater for drug crimes than for non-drug crimes. They also show that the predictability for non-drug crimes becomes nonsignificant after controlling for prior risk factors, alcohol intoxication and use of other illegal drugs. The analyses are neat and clear. While generally welcoming this excellent paper I wish to raise some issues, and I will divide these into ‘methodological’ and ‘substantive’.