Measuring Diurnal Cortisol Change in a Population-Based Field Study: Don’t Try This at Home (Alone)

Carolyn Tucker Halpern, University of North Carolina at Chapel Hill
Eric A. Whitsel, University of North Carolina at Chapel Hill
Brandon Wagner, University of North Carolina at Chapel Hill

Biomarkers are increasingly used in population-based field research. This paper describes evaluation of a three-sample, one-day, post-interview protocol for collecting saliva and assaying cortisol concentrations in the National Longitudinal Study of Adolescent Health (Add Health) Wave IV Pretest. The Pretest included 193 Add Health respondents, 97% of whom agreed to collect and return samples by mail. Only 88% of consenters returned samples. Of samples received, 25% were missing self-reported collection times. For respondents not missing times, 73% reported adhering to protocol, but only 43% verifiably adhered to key morning procedures designed to estimate cortisol response to awakening. Embedded experiments indicated no consistent effects of monetary incentives or respondent awareness of monitoring on adherence. The short-term reliability of cortisol was low, partly due to protocol non-adherence. Findings indicate that population-based field studies should carefully evaluate the feasibility of, adherence to, and reliability of biomarkers assayed in unsupervised, participant-conducted biospecimen collection protocols.