Analyses were previously conducted to estimate the heritability of the three phenotypes of interest: DSM-IV cannabis dependence, cannabis craving, and irritable/anxious during cannabis withdrawal using SOLAR [http://solar.sfbrgenetics.org/] [Almasy and Blangero, 1998] [Ehlers et al., unpublished work]. Participant's age at the time of evaluation and sex were evaluated as potential covariates and retained if they accounted for at least 5% of the total variance. The total additive genetic heritability (h2) and its standard error were estimated, and the probability that h2 was greater than zero was determined using a Student's t-test for each scale, and all three phenotypes were found to be heritable and as such suitable for linkage analyses.
