Sibling-parent SIS-R psychosis association as a function of sibling cannabis use, assessed as cannabis frequency use (top) and cannabis urinalysis (bottom).

Depicted are models of SIS-R psychosis in the sibling as dependent variable and sibling cannabis use, parental SIS-R psychosis and their interaction as independent variables, adjusted for age, sex, ethnic group and parental cannabis lifetime use. Stratified associations were derived from the model by linear combination of effects.