In Reply We thank Wang et al for their comments on our meta-analysis.1 The authors suggest further exploration of between-study heterogeneity, specifically by subgrouping studies according to sample size and parental education as well as by regressing the frequency and duration of electronic cigarette (e-cigarette) use on a continuous scale. While we agree with Wang et al that our summary and subgroup analyses revealed high levels of between-study heterogeneity, we note that 19 of 21 studies included in our meta-analysis showed a clear positive association between e-cigarette and marijuana use. The 2 remaining studies (one smaller and one larger study) contained odds ratios for the association between e-cigarette and marijuana use that were very close to 1, with confidence intervals extending on both sides of the null. Although it is true that small studies tend to provide more extreme effects than large studies, in our case, the smaller studies provided modest effects compared with the larger studies included in our analysis. Thus, it appears unlikely that performing additional subgroup analyses and regressions would significantly alter the associations we found. We also used the most conservative frequency of e-cigarette and marijuana use available in each study (ie, lifetime use) to form use and nonuse groups. Given this, the association we found would likely be strengthened by conducting additional regressions based on frequency and duration of use. Because participants tend to underreport rather than overreport their recreational drug use, it is possible that the true effect is even higher than the estimated one. Finally, and perhaps, most importantly, data on parental education and frequency and duration of use were not available for many of the studies included in our study.
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Chadi N, Levy S. Underexplored Heterogeneity and Publication Bias for the Electronic Cigarette and Marijuana Use Association—Reply. JAMA Pediatr. Published online February 17, 2020. doi:10.1001/jamapediatrics.2019.6093
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