Purpose: The objective of our study was to assess the effects of requiring parental consent upon study participation and self-reported substance-related problems among 14-18-year-olds.
Methods: This was a secondary analysis of combined data from two similar studies of adolescent substance use that recruited participants from the same adolescent clinic at Children's Hospital Boston. Study 1 waived parental consent, whereas Study 2 required parental consent. The combined dataset included demographic characteristics and Car, Relax, Alone, Forget, Friends, Trouble (CRAFFT) study screening test responses. The CRAFFT is an orally administered screen that yields a score from 0-6 and that has been shown to be a valid and reliable measure of risk for substance-related problems.
Results: The participation refusal rate in Study 1, where consent was waived, was 19.7% (132 of 670 eligible individuals) and in Study 2 (243 of 411 eligible individuals), where consent was required, it was 59.1% (p < .0001). Participants did not differ significantly with respect to gender and age but did differ by self-identified race/ethnicity between the two studies. Because the CRAFFT score distributions were highly skewed, we used the nonparametric Mann-Whitney U test for differences in mean rank. The mean rank in Study 1 was significantly higher than in Study 2 (mean rank 362 vs. 325, p = .02). After controlling for age, gender, and race/ethnicity, the adjusted proportional odds ratio for a one-point increase in CRAFFT score was 1.47 (CI 1.03, 2.10) for Study 1 compared with Study 2.
Conclusions: The research requirement of parental consent may result in substantial self-selection bias towards a lower risk sample.