Correspondence between adolescent and informant reports of substance use: Findings from the Philadelphia Neurodevelopmental Cohort

- Large study of agreement between adolescent and informant reports of substance use
- Agreement ranged from low (κ = 0.007, inhalants) to moderate (κ = 0.414, marijuana).
- ~ 70% of collaterals were unaware of adolescent alcohol or marijuana use.
- > 90% of collaterals were unaware of adolescent cocaine, inhalant, or stimulant use.
- Adolescent age, sex, psychopathology, substance use patterns related to agreement

Inclusion of collateral informant reports is common in adolescent psychopathology research and clinical assessment, yet few studies have examined agreement on ratings of adolescent substance use or factors that may be associated with reporter agreement. The present study aimed to extend prior work on the correspondence between adolescent and informant reports of adolescent substance use with data from a large (n = 5214), diverse, community-based sample of youth aged 11-17 (mean age = 14.53, SD = 1.98; 52% female). Specifically, we examined: (a) agreement between adolescent and collateral informant reports of adolescent use of alcohol, marijuana, cocaine, inhalants, and stimulants and (b) potential correlates of reporter agreement. Agreement ranged from low (κ = 0.007, p = 0.053) for inhalant use to moderate (κ = 0.414, p < 0.001) for marijuana use. Disagreements were mainly driven by collateral underestimation of adolescent substance use. Older adolescent age was associated with poorer agreement across all substances (Odds Ratios [ORs] ≤ 0.80, ps < 0.05) except inhalants (OR = 1.28, p < 0.001). Reporter agreement on alcohol and marijuana use was lower for male than female adolescents (ORs ≤ 0.85, ps < 0.05). Adolescent psychopathology was associated with poorer agreement on all substances (ORs ≤ 0.62, ps < 0.01). For alcohol and marijuana, past year frequency of use was associated with better reporter agreement (ORs ≥ 1.54, ps < 0.001). For marijuana, older age at first use was related to poorer agreement (OR = 0.81, p = 0.01). Our results suggest that collateral reports of adolescent substance use may be ineffective proxies for adolescent self-reports in community samples, particularly for low base rate substances. Findings also highlight important factors to consider when collecting substance use information from multiple informants.