Analyzing data from nonrandomized group studies

By Jeremy Bray, William Schlenger, Gary Zarkin, Deborah Galvin

Researchers evaluating prevention and early intervention programs must often rely on diverse study designs that assign groups to various study conditions (e.g., intervention versus control). Although the strongest designs randomly assign these groups to conditions, researchers frequently must use nonrandomized research designs in which assignments are made based on the characteristics of the groups. With nonrandomized group designs, little guidance is available on how best to analyze the data. We provide guidance on which techniques work best under different data conditions and make recommendations to researchers about how to choose among the various techniques when analyzing data from a pre-test/post-test nonrandomized study. We use data from the Center for Substance Abuse Prevention’s Workplace Managed Care initiative to compare the performance of the various methods commonly applied in quasi-experimental and group assignment designs.


Bray, J., Schlenger, W., Zarkin, G., & Galvin, D. (2008). Analyzing data from nonrandomized group studies. (RTI Press Publication No. MR-0008-0811). Research Triangle Park, NC: RTI Press.

© 2019 RTI International. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.


Jeremy BrayJeremy W. Bray, PhD, is an RTI International Senior Fellow in health economics and the principal investigator of the Data and Methodological Coordinating Center for the NIH/CDC Work, Family & Health Network (WFHN).

William SchlengerWilliam E. Schlenger, PhD, formerly of RTI, is a Principal Scientist at Abt Associates Inc.

Gary ZarkinGary A. Zarkin, PhD, has led or participated in several projects involving the economic analysis of drug treatment, prevention, and studies of workplace substance abuse. Dr. Zarkin has published several papers on the cost, cost-effectiveness, and the benefit-cost of substance abuse interventions. He is currently the PI on a grant funded by NIAAA to estimate the cost and cost-effectiveness of the COMBINE intervention, and he is the project director of the State Outcomes Measurement and Management System contract with SAMHSA. He previously led the development of a new method to estimate the cost of services for methadone treatment. Before coming to RTI, Dr. Zarkin was an assistant professor of economics and a research associate professor of statistics at Duke University. He has published on economics, substance abuse, and health service topics in a wide range of professional journals.

Deborah GalvinDeborah M. Galvin, PhD, is the Workplace Prevention Research Manager for the Division of Workplace Programs at the Substance Abuse and Mental Health Services Administration’s Center for Substance Abuse Prevention. She received her doctorate in sociology/criminology from the University of Pennsylvania, has over 20 years’ experience in social science research, and is widely published at the national and international levels. Dr. Galvin has been responsible at SAMHSA for the Young Adults in the Workplace program, Workplace Managed Care, and a variety of programs related to prevention of substance abuse and related concerns including comorbidity, violence, and the integration of emotional, behavioral, and physical health issues along with related methodological and research issues. She also is an adjunct professor at George Washington University and the University of Maryland.

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