Challenges of measuring diurnal cortisol concentrations in a large population-based field study

Longitudinal examinations of associations between daily stress, diurnal cortisol concentrations, and physiological parameters in population-based studies are needed. This study evaluates issues related to consent, collection, and protocol adherence for a low-burden saliva collection protocol.

In the 2007 pretest (n=193) for Wave IV of the National Longitudinal Study of Adolescent Health (Add Health) a three-sample, one-day, unsupervised saliva collection protocol was pilot tested. Embedded experiments allowed for examination of adherence and effects of monetary incentives.

Although most (97%) study participants consented to collection, only about 80% actually mailed back samples. Use of a time-stamping TrackCap allowed comparison of self-reported and stamp-recorded collection times. Of returned samples, self-report of collection time was missing for about a quarter, and only about one in three respondents (of those for whom adherence was calculable) fully adhered to the collection protocol, indicating significant potential for bias. Consent, return, and protocol adherence were unrelated to key sociodemographic characteristics, and did not improve with higher monetary incentives or knowledge of being monitored.

Despite the relatively low-burden collection protocol and use of multiple strategies thought to improve collection and protocol adherence, response and adherence were poor, leading to a decision to drop cortisol measurement from the Wave IV Add Health protocol. Large field studies should carefully evaluate the feasibility of collection and protocol adherence for unsupervised collection protocols before implementing costly, and potentially unusable, biological measurements.