242086 Designing Longitudinal Studies with Repeated Measures: The Case of Salivary Cortisol in the Multi-Ethnic Study of Atherosclerosis

Monday, October 31, 2011: 10:50 AM

Meihua Wu, MS , Department of Biostatistics, University of Michigan, Ann Arbor, MI
Brisa N. Sanchez, PhD , Department of Biostatistics, University of Michigan, Ann Arbor, MI
Trivellore Raghunathan, PhD , Department of Biostatistics, University of Michigan, Ann Arbor, MI
Ana V. Diez-Roux, PhD, MD , Department of Epidemiology, University of Michigan, Ann Arbor, MI
Defining the times at which samples are collected is an important aspect of longitudinal study design. Unfortunately, sampling times are often determined based on convenience and their optimality is seldom established statistically. Such convenient sampling strategy is likely to undermine the statistical efficiency of the study, especially in those cases where the response profile over time is nonlinear. Using the example of salivary cortisol, which exhibits a the nonlinear shape across the days, we discuss an approach for identifying efficient sampling protocols for studies where longitudinal measurements are collected. We model the response curves using conditionally linear mixed models, which allow some parameters to be nonlinear and accommodate flexible shapes of the longitudinal process. Our approach incorporates multi level random effects to account for between- subject and between-day variability commonly seen in epidemiological studies of the stress response. Furthermore, we propose a framework to include overall study costs when choosing the best sampling protocol.

Learning Areas:
Biostatistics, economics
Social and behavioral sciences

Learning Objectives:
Discuss the design of population-based epidemiology studies on salivary cortisol

Keywords: Statistics, Stress

Presenting author's disclosure statement:

Qualified on the content I am responsible for because: I am qualified to present because I am the first author of the manuscript associated with this presentation.
Any relevant financial relationships? No

I agree to comply with the American Public Health Association Conflict of Interest and Commercial Support Guidelines, and to disclose to the participants any off-label or experimental uses of a commercial product or service discussed in my presentation.