The parental knowledge measure was the sum score of four adolescent self-report items adapted from Chassin and colleagues [33] about the degree to which their parents know about their daily plans, activities and whereabouts, how they spend their money, and where/who they are with when not at home. Responses were made on a 4-point scale ranging from almost always to rarely or never, and were summed such that high scores indicate low parental knowledge (more risk; range 4–16).
