The accuracy of young adult cannabis users' perceptions of friends' cannabis and alcohol use.

OBJECTIVE: Understanding the complex influence of peers on young adult substance use is an important component of intervention research and is challenging methodologically. The false consensus theory suggests that individuals falsely attribute their own substance use behaviors onto others, producing biased data.

METHODS: We tested this theory with 39 young adults who had a cannabis use disorder and a mean age of 20. Participants (egos) recruited three of their close friends (alters). Egos reported their past 30-day cannabis and alcohol use and their perceptions of alters' use. Alters also reported their actual past 30-day cannabis and alcohol use.

RESULTS: Results demonstrated that egos were very accurate in their perceptions of the frequency of alters' cannabis (ρ = 0.82, p < 0.001) and alcohol (ρ = 0.74, p < 0.001) use. Linear regression models predicted alters' actual cannabis and alcohol use based on egos' perceptions of alters' use, controlling for egos' own substance use. Egos' perceptions of alters' cannabis use strongly predicted alters' actual use (β = 0.80, p < 0.001, adj-R2  = 0.67), and egos' perceptions of alters' alcohol use also predicted alters' actual use (β = 0.66, p < 0.001, adj-R2  = 0.62). Egos' own substance use did not predict alters' use in either model.

CONCLUSIONS: Results provide evidence that the false consensus theory may be limited when applied to young adults with cannabis use disorder within a close-friend research framework. The results support the hypothesis that young adults are very accurate in their perceptions of the frequency of close friends' substance use and that these perceptions are independent of egos' own use. These findings support the continued use of ego-centric reported close peer substance use for understanding peer effects.