Ecological salivary cortisol analysis - Part 2: Relative impact of trauma history, posttraumatic stress, comorbidity, chronic stress, and known confounds on hormone levels

Background: Although bio-psycho-social health research is an ideal, samples adequate for complex modeling require biomarker specimens from hundreds of participants. Ecological sampling departs from laboratory study norms, with implications for analysis. Objective: To inform ecological study designs, this article compares salivary cortisol levels and effect sizes of "focal" psychiatric factors, such as trauma history, posttraumatic stress diagnosis, comorbidity, and chronic stress, and "nuisance" factors, including endocrine disorders and medications and physiological factors such as gestational age and smoking. Study Design: This is a descriptive analysis of ecologically collected cortisol specimens, assayed in an ongoing perinatal psychobiological study, addressing methodological considerations. Results: Focal and nuisance factors are often interdependent with similar effect sizes. Careful specimen deletion decisions and model specification are needed to achieve the hoped-for external validity while maintaining internal validity. Conclusions: Results of multivariate models lend support to the validity and usefulness of an ecological approach to incorporating biomarkers in health research.