Meta-Analysis Snapshot
|
Literature Coverage Dates |
Number of Studies |
Number of Study Participants |
Meta Analysis 1 |
1998-2015 |
30 |
29513 |
Meta Analysis 1Lize and colleagues (2017) conducted a meta-analysis to examine the effectiveness of interactive, middle school–based drug prevention programs (in North America) on adolescent marijuana use. A systematic literature search was conducted to identify published and unpublished studies, using databases such as ProQuest, EBSCO, and Medline, for English-language studies from January 1998 to March 2014. Additional studies were identified from citations in prior reviews and eligible studies through April 2015. Studies included in the sample were randomized controlled trials and quasi-experimental designs of middle school–based (grades 6–8) substance use–prevention programs with interactive components (skills building and student engagement) that reported sufficient statistical information to calculate effect sizes of preventing cannabis use on adolescents ages 12–14. Studies were excluded if the sample included elementary or high school students, the primary program components were delivered in the home or in a community setting, it included program components described as extracurricular activities, it included comparison groups with another prevention program, it assessed only program completers, or attrition caused the sample groups to be nonequivalent.
Thirty studies yielding 23 independent samples were included. The studies included in the meta-analysis were conducted mainly in the United States, with one study from Canada. All but one study used random assignment of participants. Follow-up periods for the studies ranged from immediately posttreatment to 72 months, with the mean being 16 months. Sample sizes of the studies ranged from 42 to 5,756 participants, with the mean being 1,613 participants. Gender breakdown was approximately equal between boys and girls in study samples. Racial composition ranged from 97 percent White to 99 percent nonwhite samples. Studies were conducted in urban (9 studies), rural (4 studies), and mixed (10 studies) settings.
Study interventions were Project ALERT (5 studies), Life Skills Training (3 studies), All Stars (3 studies), and other program curricula (12 studies). Intervention sessions ranged from 3 to 40, with the mean being 17 sessions. Booster sessions were given in 10 studies between 6 months to 1 year postintervention. Interventions were delivered during school (17 studies), after school (2 studies), and a combination of during and after school activities (4 studies). Interventions were delivered by teachers (10 studies), a clinician (9 studies), a police officer (1 study), a trained adult with a peer leader (1 study), or a volunteer from the community (1 study). Comparison samples included students who received treatment as usual (11 studies), no programming (10 studies), or health information only (2 studies).
The meta-analysis looked at the following outcomes: posttreatment marijuana use, intent to use, and refusal skills. For the CrimeSolutions review of this meta-analysis, the outcome of interest was posttreatment marijuana use from random controlled designed studies (21 independent samples from 29 studies). Effect sizes (Cohen’s d) were calculated from continuous measures, and dichotomous measures were converted to the d index. Program effects were measured by computing the standardized mean difference effect size and weighted by the pooled standard deviations of the treatment and comparison groups. Individual effect sizes were combined using random effects models employing inverse variance weights with each effect size. Random effects models were used to account for possible variation other than sampling error among effect sizes as well as heterogeneity in programs and participants. To account for clustered studies, an effective sample size was estimated for each clustered sample to avoid inflating the effect size based on clustering.
Moderator analysis was conducted on the pooled effect size for any marijuana use with the program and study characteristic variables. For results of the moderator analysis, see Other Information.