Enhancing gender and ethnic representativeness of NCHA-II data with survey weights: The examples of substance use prevalence and state marijuana legalization

Abstract

Objective

We evaluated how applying post-stratification sampling weights to National College Health Assessment II (NCHA-II) data affects estimates of substance use prevalence and tests of medical and recreational marijuana legalization (MML and RML) effects. Participants/Methods: We constructed weights for Fall 2015 and Spring 2016 surveys (n = 90,503) using population information on U.S. undergraduates’ gender and race/ethnicity and three institutional characteristics (region, city population, public/private). We estimated substance use prevalence (e.g., e-cigarettes, prescription opioid misuse) and compared 30-day marijuana use rates in states with RML, MML, or neither policy. Results: When unweighted versus weighted data were used, prevalence estimates did not differ appreciably; conclusions from logistic regressions were similar (weighted 30-day marijuana use rates among undergraduates in RML, MML, and non-ML states were 30.0%, 20.3%, and 16.3%, respectively) but effect sizes differed. Conclusions: The value of using weighted NCHA-II data depends on the analysis and the precision required for the research questions.

Keywords:

• College students
• ethnicity
• post-stratification weights
• recreational marijuana legalization
• representativeness
• substance use

Acknowledgments

The authors thank Mary Hoban and Christine Kukich for their consultation, expertise, and assistance. The opinions, findings, and conclusions presented/reported in this article/presentation are those of the authors, and are in no way meant to represent the corporate opinions, views, or policies of the American College Health Association (ACHA). ACHA does not warrant nor assume any liability or responsibility for the accuracy, completeness, or usefulness of any information presented in this article/presentation.

Conflict of interest disclosure

The authors have no conflicts of interest to report. The authors confirm that the research presented in this article met the ethical guidelines, including adherence to the legal requirements, of the United States and was deemed exempt by the Oregon State University Institutional Review Board.

Notes

1 Unweighted and weighted estimates (standard errors) were 0.286 (0.0042) and 0.300 (0.0048) for RML, 0.196 (0.0018) and 0.203 (0.0028) for MML, and 0.152 (0.0021) and 0.163 (0.0033) for non-ML states.

Additional information

Funding

This research was funded by grants from the John C. Erkkila, M.D. Endowment for Health and Human Performance and the Medical Research Foundation of Oregon.