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Figure.  Event Study Analysis
Event Study Analysis

Each panel reports weighted estimates from a separate logistic regression based on biennial data from the national Youth Risk Behavior Surveys (1993-2019) including 191 923 participants. Estimated odds ratios (ORs) of current marijuana use (and their 95% CIs) are reported. ORs were adjusted for individual-level characteristics (age, sex, grade, and race), whether marijuana use and possession were decriminalized in the respondent’s state, the presence of a state-level 0.08 blood alcohol concentration law, the state beer tax, state income per capita, state unemployment rate, state and survey wave (ie, year) indicators. Values on the horizontal axis reflect survey waves since legalization came into effect. The omitted category was 1 survey wave prior to legalization going into effect.

Table.  Estimates of the Association of Enactment of Marijuana Legalization Laws With Adolescent Marijuana Use
Estimates of the Association of Enactment of Marijuana Legalization Laws With Adolescent Marijuana Use
1.
Committee on Substance Abuse, Committee on Adolescence; Committee on Substance Abuse Committee on Adolescence.  The impact of marijuana policies on youth: clinical, research, and legal update.  Pediatrics. 2015;135(3):584-587. doi:10.1542/peds.2014-4146PubMedGoogle ScholarCrossref
2.
Anderson  DM, Hansen  B, Rees  DI, Sabia  JJ.  Association of marijuana laws with teen marijuana use: new estimates from the Youth Risk Behavior Surveys.  JAMA Pediatr. 2019;173(9):879-881. doi:10.1001/jamapediatrics.2019.1720PubMedGoogle ScholarCrossref
3.
Jones  CM, Underwood  JM, Volkow  ND.  Challenging the association of marijuana laws with teen marijuana use.  JAMA Pediatr. 2020;174(1):99. doi:10.1001/jamapediatrics.2019.4235PubMedGoogle ScholarCrossref
4.
Anderson  DM, Rees  DI, Sabia  JJ.  Challenging the association of marijuana laws with teen marijuana use-reply.  JAMA Pediatr. 2020;174(1):99-100. doi:10.1001/jamapediatrics.2019.4238PubMedGoogle ScholarCrossref
5.
Anderson  DM, Rees  DI. The public health effects of legalizing marijuana. NBER Working Paper No. 28647. Accessed August 13, 2021. https://www.nber.org/papers/w28647
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    2 Comments for this article
    EXPAND ALL
    Methodologic Concerns
    Emmet Power, MB BCh MRCPsych | Royal College of the Surgeons of Ireland (RCSI) University of Medicine & Health Science
    The main findings of Anderson el al.’s Research Letter are that cannabis use in youth decreases after introduction of medical marijuana and recreational marijuana laws (1). We have a number of questions and concerns about the report.

    The authors write that their report is STROBE-compliant but STROBE reporting standards recommend both unadjusted and adjusted estimates and outcome events be reported, which they are not (2). The base models are said to have 63 covariates. Furthermore, in the analysis of state data only it is unclear whether there is a base category or whether the constant terms were removed,
    as “all 50 states” have been covaried for according to the table and figure footnotes. Clarification is needed around this question as it unclear whether these results represent perfect multicollinearity. Furthermore, Washington and Oregon have never contributed representative data, and Minnesota has never participated. This research question requires representative data. Following this we observe deviation from the CDC’s guidance on conducting analysis with YBRS data: pooling national and state level data is not sound practice (3). Furthermore, conducting analysis at a state level on national data, which is representative of national prevalence rather than state prevalence of marijuana use appears to be flawed. It is also recommended that when pooling state level data, the data are weighted in order for the analysis to be representative of the population (3). This was not done; in both the table and figure footnotes the authors state that unweighted estimates were used in state level data analysis.

    In terms of their marijuana use predictor variable, the authors appear to have dichotomized a single ordinal variable twice (4). Within YBRS there are six ordinal response options to a question pertaining to past month marijuana use. With increases in marijuana potency a more rational analytic decision would be to examine daily usage or greater (5).

    Finally, the premise of this research letter is to analyze state level policies. This is problematic for 2 reasons: marijuana sales may remain illegal in certain counties within legalized states and this is unaccounted for; and between-state variability in legislation and implementation cannot be accounted for by uniform lags and leads.

    We therefore remain circumspect about the methodology of this study and the conclusions it draws. Marijuana is an addictive drug, and it disproportionately harms young people (5). More credible research is needed on this question.

    References

    1. Anderson DM, Rees DI, Sabia JJ, Safford S. Association of Marijuana Legalization With Marijuana Use Among US High School Students, 1993-2019. JAMA Netw. Open. 2021;4(9);e2124638.

    2. Von Elm E, Altman DG, Egger M, Pocock SJ, Gøtzsche PC, Vandenbroucke JP. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies. Bull World Health Organ. 2007;85:867-72.

    3. Centre for Disease Control. Combining YRBS Data Across Years and Sites. https://www.cdc.gov/healthyyouth/data/yrbs/pdf/2019/2019_YRBS_combining_data.pdf Accessed October 6, 2021.

    4. Centre for Disease Control. YBRS questionnaire content – 1991-2019. https://www.cdc.gov/healthyyouth/data/yrbs/pdf/2019/YRBS_questionnaire_content_1991-2019.pdf Accessed October 6, 2021.

    5. Smyth BP, Cannon M. Cannabis legalization and adolescent cannabis use: explanation of paradoxical findings. J Adolesc Health. 2021;69(1);14-5.

    CONFLICT OF INTEREST: None Reported
    READ MORE
    Methodologic Concerns
    Eli Rapoport, BS and Coauthors | NYU Grossman School of Medicine
    We read with great interest the research letter by Anderson et al. (1). Unfortunately, we have several concerns about the validity of the study and its findings.

    Several of the report’s authors previously published a study in JAMA Pediatrics with a very similar methodology (2). Both studies pooled national and state YRBS cohorts to investigate whether recreational and medical marijuana laws are associated with teen marijuana use. In response to their earlier study, we and others wrote letters to the editor identifying substantial methodological flaws (4-8). Although the more recent study addresses some of these flaws, two substantial issues
    persist:

    1. The CDC explicitly warns against pooling national and state data because underlying person-level weights are different and there is overlap between national and state YRBS data such that some students could be represented more than once (3). Although the authors had previously been cautioned about this, they once again pooled these datasets, undermining the assumptions of their statistical models and thus yielding unreliable estimates (4,5).

    2. Anderson et al. do not account for YRBS survey weighting, limiting the generalizability of their findings.

    For these reasons, we believe the estimates generated from the pooled data in this study are not valid. Additionally, the estimates from the separate national and state YRBS analyses are not adequately generalizable due to the failure to use survey weights.

    Despite the issues noted above, we fear that this research letter will be used to inform debates on the merits and potential consequences of marijuana legalization. Moreover, we are concerned that researchers may model future analyses on this study, leading to a cascade of studies with flawed methodologies.

    Sincerely,

    Eli Rapoport
    NYU Grossman School of Medicine

    Sarah A. Keim, PhD, MA, MS
    Nationwide Children’s Hospital

    Andrew Adesman, MD
    Cohen Children’s Medical Center

    Christopher M. Jones, PharmD, DrPH, MPH
    National Center for Injury Prevention and Control, Centers for Disease Control and Prevention

    J. Michael Underwood, PhD
    Division of Adolescent and School Health, Centers for Disease Control and Prevention

    Nora D. Volkow, MD
    National Institute on Drug Abuse


    References

    1. Anderson DM, Rees DI, Sabia JJ, Safford S. Association of Marijuana Legalization With Marijuana Use Among US High School Students, 1993-2019. JAMA Netw Open. 2021;4(9):e2124638.

    2. Anderson DM, Hansen B, Rees DI, Sabia JJ. Association of Marijuana Laws With Teen Marijuana Use: New Estimates From the Youth Risk Behavior Surveys. JAMA Pediatr. 2019;173(9):879–881.

    3. US Centers for Disease Control and Prevention. Youth Risk Behavior Surveillance System (YRBSS). Combining YRBS Data Across Years and Sites. Available at: https://www.cdc.gov/healthyyouth/data/yrbs/pdf/2017/2017_YRBS_combining_data.pdf. Accessed October 21, 2019.

    4. Jones CM, Underwood JM, Volkow ND. Challenging the Association of Marijuana Laws With Teen Marijuana Use. JAMA Pediatr. 2020;174(1):99.

    5. Rapoport E, Keim SA, Adesman A. Challenging the Association of Marijuana Laws With Teen Marijuana Use. JAMA Pediatr. 2020;174(1):98–99.

    6. Miller CL. Challenging the Association of Marijuana Laws With Teen Marijuana Use. JAMA Pediatr. 2020;174(1):96–97.

    7. Kamer R. Challenging the Association of Marijuana Laws With Teen Marijuana Use. JAMA Pediatr. 2020;174(1):97–98.

    8. Cannon M. Challenging the Association of Marijuana Laws With Teen Marijuana Use. JAMA Pediatr. 2020;174(1):97.
    CONFLICT OF INTEREST: None Reported
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    Research Letter
    Substance Use and Addiction
    September 7, 2021

    Association of Marijuana Legalization With Marijuana Use Among US High School Students, 1993-2019

    Author Affiliations
    • 1Department of Agricultural Economics and Economics, Montana State University, Bozeman
    • 2Department of Economics, Universidad Carlos III de Madrid, Madrid, Spain
    • 3Center for Health Economics and Policy Studies, San Diego State University, San Diego, California
    JAMA Netw Open. 2021;4(9):e2124638. doi:10.1001/jamanetworkopen.2021.24638
    Introduction

    Thirty-six states have legalized medical marijuana, and 18 states have passed recreational marijuana laws (RMLs). Organizations such as the American Academy of Pediatrics are concerned that legalization will encourage youth marijuana use.1 Marijuana use during adolescence may adversely affect areas of the prefrontal cortex that control important cognitive processes.1

    Using data from the Youth Risk Behavior Survey (YRBS) for the period 1993 to 2017, in a previous study with 3 of us as authors (D.M.A., D.I.R., and J.J.S.),2 we reported that RML adoption was associated with an 8% decrease in the odds of marijuana use among high school students. However, that study had prelegalization and postlegalization data from only 7 states and pre- and post-recreational sales data from only 3 states, limiting generalizability of the results. In addition, we had also reported unweighted estimates based on pooled national and state YRBS data, which we had subsequently been advised was not appropriate for the following reasons: (1) “Pooling national and state YRBS data is inappropriate because underlying person-level weights are different, and there is some overlap between national and state YRBS data; thus, a student could be represented more than once. The YRBS codebook explicitly warns against combining these data.” and (2) “YRBS data are designed to be weighted to capture representative populations.”3 To address this concern, we provided weighted estimates of the association between RMLs and marijuana use among teenagers and linked to these estimates in a Letter in reply.4

    Using data from the YRBS for the period 1993 to 2019, this study provides updated and weighted, unpooled national and state YRBS-based estimates of the association between legalization and adolescent marijuana use.

    Methods

    National and state YRBS data from 1993 to 2019 were analyzed separately. Data pre- and post-RML enactment were available from 10 states; 7 states contributed more than 1 wave of post-RML data, and these same 7 states contributed data to the YRBS before and after the first marijuana dispensary sales began. Data on preenactment and postenactment of medical marijuana laws (MMLs) were available from 29 states. Ethical review was not required because analyses of secondary, deidentified data are considered exempt from requiring institutional review board approval by the San Diego State University Institutional Review Board. This report attempted to follow the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guidelines.

    Effective legalization dates come from the report by Anderson and Rees.5Current marijuana use was defined as any use in the past 30 days, and frequent marijuana use was defined as use at least 10 times in the past 30 days.

    National and state YRBS data on marijuana use were analyzed separately. Weighted multivariable logistic regression was used to estimate the association between legalization and marijuana use. To control for time-invariant factors at the state level and common trends, all models were adjusted for state and survey wave indicators. Alternative models were further adjusted for individual- and state-level characteristics; event-study estimates were produced by replacing the RML and MML indicators with leads and lags. Two-sided hypothesis tests were used, and estimates were considered significant if P < .05. Analyses were conducted with Stata statistical software version 16.1 (StataCorp).

    Results

    Among 191 923 national YRBS respondents, the mean (SD) age was 16.06 (1.23) years, 49.1% of respondents reported as female, and 61.0% reported as non-Hispanic White individuals. Among 1 418 682 state YRBS respondents, the mean (SD) age was 16.03 (1.23) years, 49.8% of respondents reported as female, and 59.0% reported as non-Hispanic White individuals.

    Based on the national YRBS data and in the fully adjusted models RML adoption was not associated with current marijuana use (odds ratio [OR], 1.01; 95% CI, 0.85-1.19) or frequent marijuana use (OR, 0.99; 95% CI, 0.78-1.26). In the fully adjusted models, MML adoption also was not associated with current marijuana use (OR, 0.94; 95% CI, 0.84-1.05) or frequent marijuana use (OR, 0.90; 95% CI, 0.74-1.10). Estimates from a separate analysis of the state YRBS data also showed no significant association of RML or MML adoption with current or frequent marijuana use (Table).

    The Figure, A, shows RML event-study estimates based on the national YRBS data. Prior to RML adoption, there was no association with marijuana use, suggesting the parallel-trends assumption held. Similarly, after legalization, there was no association with marijuana use, consistent with the results reported in the Table. The Figure, B, shows an event study for MML adoption.

    Discussion

    In this cross-sectional study using weighted national YRBS data and weighted state YRBS data, there were no significant associations between enactment of RMLs or MMLs and marijuana use among high school students. These findings differ from the previous report by Anderson et al2 that had reported estimates based on unweighted pooled national and state data based on an analytic approach not recommended by the YRBS.3 This approach could also be inappropriate if legalization had heterogeneous effects across states.3,4 Limitations of this study are inclusion of data only through 2019 and only 10 states had data on pre- and post-RML enactment. RMLs are a relatively new phenomenon, and as more recent postlegalization data become available, further research will be needed to better define the associations between RMLs and adolescent marijuana use.

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    Article Information

    Accepted for Publication: July 8, 2021.

    Published: September 7, 2021. doi:10.1001/jamanetworkopen.2021.24638

    Retraction and Replacement: This article was retracted and replaced on March 8, 2022, to fix errors in the analysis methods and results (see Supplement 1 for the retracted article with errors highlighted and Supplement 2 for the replacement article with corrections highlighted).

    Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2021 Anderson DM et al. JAMA Network Open.

    Corresponding Author: D. Mark Anderson, PhD, Department of Agricultural Economics and Economics, Montana State University, PO Box 172920, Bozeman, MT 59717-2920 (dwight.anderson@montana.edu).

    Author Contributions: Dr Sabia had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

    Concept and design: All authors.

    Acquisition, analysis, or interpretation of data: Anderson, Sabia, Safford.

    Drafting of the manuscript: Anderson, Rees, Sabia.

    Critical revision of the manuscript for important intellectual content: All authors.

    Statistical analysis: Rees, Sabia, Safford.

    Obtained funding: Anderson, Sabia.

    Supervision: Anderson, Sabia.

    Conflict of Interest Disclosures: Dr Sabia reported receiving grants from Troesh Family Foundation and Charles Koch Foundation during the conduct of the study. No other disclosures were reported.

    Funding/Support: Dr Anderson acknowledges partial support from the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health (NIH) (research infrastructure grant No. R24 HD042828), to the Center for Studies in Demography and Ecology at the University of Washington. Dr Sabia and Mr Safford acknowledge partial support from the Center for Health Economics & Policy Studies at San Diego State University, including grant funding received from the Charles Koch Foundation.

    Role of the Funder/Sponsor: The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

    Disclaimer: The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

    References
    1.
    Committee on Substance Abuse, Committee on Adolescence; Committee on Substance Abuse Committee on Adolescence.  The impact of marijuana policies on youth: clinical, research, and legal update.  Pediatrics. 2015;135(3):584-587. doi:10.1542/peds.2014-4146PubMedGoogle ScholarCrossref
    2.
    Anderson  DM, Hansen  B, Rees  DI, Sabia  JJ.  Association of marijuana laws with teen marijuana use: new estimates from the Youth Risk Behavior Surveys.  JAMA Pediatr. 2019;173(9):879-881. doi:10.1001/jamapediatrics.2019.1720PubMedGoogle ScholarCrossref
    3.
    Jones  CM, Underwood  JM, Volkow  ND.  Challenging the association of marijuana laws with teen marijuana use.  JAMA Pediatr. 2020;174(1):99. doi:10.1001/jamapediatrics.2019.4235PubMedGoogle ScholarCrossref
    4.
    Anderson  DM, Rees  DI, Sabia  JJ.  Challenging the association of marijuana laws with teen marijuana use-reply.  JAMA Pediatr. 2020;174(1):99-100. doi:10.1001/jamapediatrics.2019.4238PubMedGoogle ScholarCrossref
    5.
    Anderson  DM, Rees  DI. The public health effects of legalizing marijuana. NBER Working Paper No. 28647. Accessed August 13, 2021. https://www.nber.org/papers/w28647
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