Methods: Mind the Gap

Webinar Series

Choosing Sample Sizes for Multilevel and Longitudinal Studies Analyzed with Linear Mixed Models

April 29, 2022
Keith Muller
Keith Muller, Ph.D.

University of Florida College of Medicine

Deborah Glueck
Deborah Glueck, Ph.D.

University of Colorado School of Medicine

View the Webinar

About the Webinar

Planning a reproducible study requires selecting a sample size expected to ensure appropriate statistical power. Advances in statistical methods and free point and click software have made it easy to select a sample size for clustered and longitudinal designs with linear mixed models. The software, a suite of training modules, and reference materials are freely available online ( The software interface and training materials are aimed at health scientists, and have been validated in face-to-face and online courses. Dr. Keith Muller and Dr. Deborah Glueck discuss what the software and training cover, what they do not cover, and what they hope to add. A longitudinal randomized trial is used to illustrate the process of power analysis.

About Keith Muller

Dr. Muller is a biostatistician specializing in the design and analysis of multilevel and longitudinal research. He is the first author of two books on linear model theory and practice. He has co-authored approximately 150 peer reviewed publications, of which roughly half are collaborations in health research. Dr. Muller is a fellow of the American Statistical Association. He earned bachelor's and master's degrees in psychology from Bradley University, as well as a doctorate in quantitative psychology and a master's degree in theoretical statistics from the University of North Carolina at Chapel Hill. Postdoctoral employers have included the University of Illinois (1976-1977, Educational Methods), Bell Laboratories (1977-1978, Human Factors), the University of North Carolina (1978-2006, Biostatistics), and the University of Florida (2006-present, Health Outcomes and Biomedical Informatics). Roughly half of Dr. Muller's effort has been supported by being a co-investigator or principal investigator on National Institutes of Health (NIH)-funded research. He has also served on standing and ad hoc review panels for NIH.

About Deborah Glueck

Dr. Glueck is the senior biostatistician at the Lifecourse Epidemiology of Adiposity & Diabetes (LEAD) Center at the Colorado School of Public Health; and Professor of Pediatrics at the University of Colorado Denver School of Medicine. Dr. Glueck has an A.B. cum laude from Harvard College in mathematics, and M.S. and Ph.D. degrees in biostatistics from the University of North Carolina at Chapel Hill. She completed a post‐doctoral fellowship in health services research at Robert Wood Johnson Medical School. Dr. Glueck has a career‐long focus on power and sample size for multilevel and longitudinal studies, and the analysis of longitudinal epidemiological cohort studies and randomized controlled clinical trials. Dr. Glueck was a Multiple Principal Investigator (MPI) for an R01 for the development of novel analytic methods for lifecourse studies, including implementation and development of novel techniques to model developmental trajectories in youth (R01GM121081); was MPI of a National Library of Medicine-funded G13 grant for a book on power and sample size; and was MPI of a National Institute of General Medical Sciences-funded R25 for developing a short course and massive online open course on power and sample size.

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