A recent study investigated the relationship between alcohol and marijuana use among college students, as well as the role of skipping class on the relationship between substance use and GPA. Participants were undergraduate students at one U.S. university whose names were listed in the institution’s directory. Of the 8,471 undergraduates contacted, 13% (n = 1,104) responded and completed an online survey. The final analytic sample consisted of 946 students. Survey measures included self-reported GPA, past-year alcohol and marijuana use, demographic characteristics, and frequency of skipping class (options ranged from ‘never’ to ‘all of the time’). Results showed the average GPA for the sample was 3.21 (higher than the university-wide average), 90% reported past-year alcohol use (with 40% reported using on 40 or more occasions), and nearly half of respondents reported past-year marijuana use. The authors used bivariate correlation, ordinary least squares (OLS) regressions, and mediational analyses to examine the relationships of interest. They found both alcohol and marijuana use were significantly negatively correlated with GPA (r = -0.16, p < 0.001 and r = -0.20, p < 0.001, respectively). Respondents who reported skipping class less frequently were more likely to report having higher GPAs than those who reported skipping class frequently. Results of the OLS regressions found alcohol use significantly predicted GPA (p = 0.004), even when controlling for other variables. Male sex (p < 0.001) and non-White race (p < 0.001) both had a significant negative relationship with GPA. Results for an OLS regression with marijuana use were similar: Marijuana use alone was significantly negatively associated with GPA (p < 0.001) and marijuana use accounted for 12.7% of the variance in GPA. A third OLS regression model that included both alcohol use and marijuana use found only marijuana use was a significant predictor of GPA (p = 0.01), with a negative association between frequency of use and GPA. In this model, frequency of skipping class was the most important predictor of GPA. Results of the mediation analyses found marijuana use mediated the relationship between alcohol use and GPA, accounting for nearly half of the total effect. Skipping class was found to partially mediate the relationship between alcohol use and GPA, accounting for about 40% of the total effect. Results for marijuana use were similar: It had a significant indirect effect on GPA through the frequency of skipping class, accounting for about 35% of the total effect.
Take away: In this sample, both marijuana use and alcohol use were significantly negatively associated with GPA. Skipping class was found to partially mediate the relationships between alcohol and marijuana use on GPA, accounting for approximately one-half and one-third of the respective total effects.