Ecological salivary cortisol specimen collection - Part 1: Methodological consideration of yield, error, and effects of sampling decisions in a perinatal mental health study

Background: Current health research strives to integrate biological, psychological, and social factors consistent with ecological models. Home-based biomarker specimens are consistent with an ecological approach, but deviations from laboratory norms could affect validity of results. Objective: This article uses salivary cortisol specimens collected early in a perinatal mental health study to describe (a) return rate and returner characteristics, (b) adherence to procedures, (c) sources of laboratory error, (d) effects of deleting specimens with "nuisance" factors, and (e) effects that selection bias could have on cortisol concentration distribution. Study design: This includes methodological analysis of collection, assay, and preanalysis decision components. Results: Rates of return donot differ by participants' sociodemographic, perinatal, or psychiatric characteristics. Excluding smokers affects representativeness. Selection bias in favor of more or less disadvantaged participants affects cortisol distribution. Conclusion: The large yield of useable specimens permits multivariate modeling of cortisol level in association with health outcomes, potentially enhancing ecological validity.