The CHR Biostatistics Core provides technical expertise, programming support, and consultation to research projects on study design, data management, and data analysis. This group of investigators and researchers also assists with grant and manuscript preparation and helps others at the Center understand and interpret the results of our data analyses.

Members of the Biostatistics Core


Nancy Perrin, PhD, Senior Investigator Emeritus & Director, Biostatistics Core

Dr. Perrin is an expert in the application of multivariate statistical techniques to health outcomes. She uses a variety of designs and statistical methods in her research. Dr. Perrin came to CHR from Oregon Health & Science University, where she retains an adjunct professor appointment. A former professor and associate dean at Portland State University, she received her bachelor’s degree from University of California, Los Angeles, and her master’s and doctoral degrees from The Ohio State University.


John Dickerson, PhD, Assistant Investigator

Dr. Dickerson is a health economist and biostatistician interested in modeling patient and provider behavior related to adherence as part of observational and controlled research studies. Dr. Dickerson earned a bachelor’s degree from James Madison University, a master’s in economics from Oregon State University, and a PhD in health services research at the University of Washington with dual concentrations in health economics and statistics.


Michael Leo, PhD, Investigator

As a consulting biostatistician, Dr. Leo uses a variety of research designs including quasi-experimental (longitudinal and cross-sectional), community-based participatory, and clinical trials. He is experienced with a variety of statistical techniques, such as general and generalized linear models, structural equation modeling, hierarchical linear modeling, and psychometrics. He received his PhD from Portland State University in systems science in the areas of industrial and organizational psychology and quantitative methods.


Gabriela Rosales, MS, Biostatistician

Ms. Rosales provides statistical consultation, assists in proposal development, conducts statistical analyses, and helps organize a Biostatistics Seminar Series. She has a master's degree in statistics and was a biostatistician at the Mayo Clinic before joining CHR. She has expertise in a variety of statistical analyses including survival analysis, propensity scores, generalized estimating equations, and power analyses.


Ning Smith, PhD, Senior Investigator

Dr. Smith is a consulting biostatistician. Her research areas include obesity in children and young adults and herpes zoster vaccination in an elderly population. She also studies the use of electronic medical and administrative records in research. She uses statistical methods such as multiple comparisons, multivariate analyses, logistic regression, longitudinal data analysis, mixed effects and generalized linear models, survival analysis, and factor analysis. She received a PhD and MS in biostatistics from the University of Michigan and a BS in economics from Nankai University in Tianjin, China.


William Vollmer, PhD, Senior Investigator Emeritus

Dr. Vollmer conducts research in the areas of blood pressure and weight, dental caries, the epidemiology and management of asthma and pulmonary disease, and numerous others. He also leads a number of coordinating centers for which he steers the direction of multi-site trials and works collaboratively with other trial investigators to resolve complex protocol-related issues. Dr. Vollmer received his PhD in biostatistics from the University of Washington.

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