The independent variable was whether or not a city had a dispensary ban and was determined by the city policy that was in effect when the count of dispensaries per city was obtained in September 2016. The research question was broken up into three testable hypotheses: H2.1) there is a direct relationship between city dispensary bans and the number of dispensaries in a city, where city dispensary bans are associated with lower numbers of dispensaries; H2.2) fewer dispensaries in a city is associated with less availability of marijuana to high school students ; H2.3) the effect of city dispensary bans on adolescent marijuana use is dependent on them having a suppressing effect on the number of dispensaries operating in a city. To test the hypotheses associated with Research Question 3, I used a variable that indicated whether students perceived great risk from frequent marijuana use as the mediating variable and controlled for factors known to influence marijuana use among adolescents, such as gender, race/ethnicity, and social/economic status. As with Research Question 2, the independent variable was whether the city had a dispensary ban and was determined by the city policy that was in effect when the count of dispensaries per city was obtained in September 2016. The outcome variable was self-reported student marijuana use . Research Question 3 was broken up into three testable hypotheses: H3.1) there is a direct relationship between city dispensary bans and students’ perceptions of the risk of frequent marijuana use, so that dispensary bans are positively associated with perceived risk; H3.2) there is a direct inverse relationship between students’ perception of the risk of frequent marijuana use and their likelihood of using marijuana,plant benches so that students who perceive great risk from frequent marijuana use are less likely to use marijuana; and H3.3) the relationship between city dispensary bans and student marijuana use is dependent on dispensary bans being associated with greater perceptions of the risk of frequent marijuana use among students and an inverse relationship between perceptions of risk and student marijuana use.
To assess the mediating effect of perceived risk on student marijuana use and test hypothesis H3.1 I calculated the association between city dispensary bans and whether students perceived great risk from frequent marijuana use. If the coefficient was significant and positive, then H3.2 was supported. The second step was to test H3.3 by establishing whether there was a significant positive association between the moderating variable and the outcome variable . This model contained both the focal independent variable and the moderator . Finally, using the same regression model, I assessed the net direct effect of the focal independent variable on the outcome variable while accounting for the indirect effect of the moderator . I hypothesized that students’ perceptions of risk mediated the effect of city policy to some degree, and that the direct effect of the focal relationship coefficient would therefore decrease in magnitude when I controlled for students’ perceptions of risk. To test whether the mediation effect of students’ perceptions of risk was statistically significant from zero, I used a Sobel Test. Because perceived risk was measured at the individual level, I used the single level of the model to test the mediated relationship. To test the hypotheses associated with Research Question 4, I used a continuous measure of the distance in miles between the school and the closest dispensary in LA County as the mediating variable and controlled for factors known to influence marijuana use among adolescents, such as gender, race/ethnicity, and social/economic status. As with Research Questions 2 – 3, the independent variable was whether or not a city had a dispensary ban and was determined by the city policy that was in effect when the count of dispensaries per city was obtained in September 2016. The outcome variable was self-reported student marijuana use .
Research Question 4 was similarly broken up into three testable hypotheses: H4.1) there is a direct relationship between city dispensary bans and the proximity of dispensaries to the students’ high school, so that dispensary bans are associated with longer distances from dispensaries; H4.2) there is a direct relationship between the proximity of dispensaries and students’ likelihood of using marijuana, so that the lesser the distance between the school and the closest dispensary, the greater a student’s likelihood to use marijuana; and H4.3) the relationship between city dispensary bans and high school students’ marijuana use is mediated to some degree by dispensary bans being associated with a longer distance between dispensaries and schools. To assess the mediating effect of the distance to the closest dispensary located within a mile of their high school on students’ marijuana use, I first tested hypothesis H4.1 by determining whether there was a relationship between the independent variable and the moderating variable by calculating the association between city dispensary bans and the continuous distance to the nearest dispensary within LA County. If the coefficient was significant and positive, then H4.2 was supported. The second step was to test H4.3 by establishing whether there was a significant positive association between the moderating variable and the outcome variable . This model contained both the focal independent variable and the moderator . Finally, using the same regression model, I assessed the net direct effect of the focal independent variable on the outcome variable while accounting for the indirect effect of the moderator . I hypothesized that city dispensary bans would be associated with longer distances between participants’ schools and the nearest dispensary in the County and that the association between dispensary bans and student marijuana use would be statistically significant when accounting for this factor.
I used a Sobel Test to determine whether the mediation effect of the distance to the nearest dispensary from the school was statistically significant. To test the hypotheses associated with Research Question 5, I used the number of verified dispensaries located within 2,000 feet of the students’ high schools as the mediating variable and controlled for factors known to influence marijuana use among adolescents, such as gender, race/ethnicity,gardening rack and social/economic status. I also explored whether there were any different effects for the number of unlicensed dispensaries compared to licensed dispensaries. As with Research Questions 2 – 4, the independent variable was whether or not a city had a dispensary ban and was determined by the city policy that was in effect when the count of dispensaries per city was obtained in September 2016. The outcome variable was self-reported student marijuana use . Research Question 5 was similarly broken up into three testable hypotheses: H5.1) there is a direct relationship between city dispensary bans and the number of dispensaries located within 2,000 feet of the students’ high school, such that dispensary bans are associated with less dispensaries being located within a quarter mile of the school; H5.2) there is a direct relationship between the number of dispensaries located within 2,000 feet of the school and students’ likelihood of using marijuana, so that the number of dispensaries located within 2,000 feet is positively associated with students’ likelihood to use marijuana; and H5.3) the relationship between city dispensary bans and high school students’ marijuana use is mediated to some degree by dispensary bans being more effective at preventing dispensaries from locating near schools than city policies that allow dispensaries. To assess the mediating effect of the number of dispensaries located within 2,000 feet of their high school on students’ marijuana use, I first tested hypothesis H5.1 by determining whether there was a relationship between the independent variable and the moderating variable by calculating the association between city dispensary bans and how many dispensaries were located within 2,000 feet of each school. If the coefficient was significant and positive, then H5.2 was supported. The second step was to test H5.3 by establishing whether there was a significant positive association between the moderating variable and the outcome variable . Finally, using the same regression model, I assessed the net direct effect of the focal independent variable on the outcome variable while accounting for the indirect effect of the moderator . I hypothesized that the number of dispensaries located within 2000 of their school would mediate the effect of city policy to some degree, and that the direct effect of the focal relationship coefficient would therefore decrease in magnitude when I controlled for the number of dispensaries located within 2,000 feet the school. To test whether the mediation effect of having dispensaries located near the students’ high schools was statistically significant from zero, I used Sobel Test. The analyses presented above had several important limitations.
The trend analysis relied on a series of cross-sectional surveys, so I was not able to follow the same students over time. The students surveyed were also limited to students who participated in a school-based survey, so the findings from these analyses cannot be generalized to students who are out of school. The students surveyed were also exclusively public high school students, and may have differed in substantial ways from students attending private high schools. The results of this analysis should therefore not be generalized to students attending private high schools. The results may also not be generalizable to LA County as a whole, as only 57 cities out the 88 cities in the County had schools that participated in the CHKS survey during the 2105/2016 and 2016/2017 school years. Instead, this research should be taken as evidence of the need for representative data that can be used for further study of the effects of city dispensary policies on the neighborhood-level conditions that were shown to have a significant influence on students’ marijuana use behaviors; the distance to the nearest dispensary and the number of dispensaries located within several blocks of schools. Finally, I was unable to measure compliance with city or state laws regulating business practices among dispensary owners. I could not measure efforts to enforce dispensary bans or restrictions and did not undertake tomeasure how strict city dispensary ordinances were relative to each other. Future studies of city and county dispensary ordinances should assess these factors to determine how they may mediate or moderate the effect of dispensary ordinances on local conditions that facilitate adolescent marijuana use. Although there are compelling reasons to believe the presence of dispensaries would be correlated with adolescent marijuana use, there is equally credible evidence to suggest that dispensary bans may have little effect on students’ marijuana use. For example, a notable result from the preliminary analyses presented in Chapter 4 was that rates of marijuana use increased from baseline through the 2011/2013 time point even among cities that banned dispensaries. The proportion of students in LA County attending school in a city that allowed dispensaries more than quadrupled during the study period from 3.48% in 2005/2006 to 14.45% in 2016/2017. During the same period, the proportion of students in the County reporting lifetime marijuana use declined from 30% to 25% and recent marijuana use declined from 16% to 14% . These findings suggest that whether their city allows dispensaries may not the primary determinant of rates of marijuana use among LA County high school students. For this analysis, I used a 2-level Hierarchical Generalized Linear Model with students as the level 1 variable and city as the level 2 variable to compare the proportion of students who reported lifetime and recent marijuana use among all the LA County cities that had students participating in the CHKS survey during the 2015/2016 and 2016/2017 school years. The independent variable is whether the city the students lived in/attended school in a city that allowed or banned dispensaries as of September 2016. Covariates included gender, grade, race/ethnicity, participation in after school programs, whether the student received free or low cost meals , whether one or more of the students’ parents had a college degree, and whether they attended a non-traditional school. This analysis uses two pooled years of CHKS survey data, for a combined total of 101,521 students. Combining two school years of CHKS data was necessary because most schools administer the survey every other year and therefore, in any given year half of them are off cycle. More importantly, preliminary analyses indicated that the average number of participants from Los Angeles schools on odd years was approximately double the average from even years.