Population-scale measurements of psychological stress during the transition to adulthood are generally constrained to either self-reported measures or biomarkers that reflect only recent hours of brain response to stress. Recent breakthroughs in the use of hair to obtain stable measures of cortisol?a biomarker for the impact of stress on the human brain?has the potential to revolutionize this science. Hair-based cortisol provides a reliable measure of brain-experienced stress levels for the three months directly preceding collection of a hair sample. Laboratory processes for cortisol analysis of hair are now available at a scale that can be used for general population research. Like some other biomarkers, hair could be collected by study participants themselves, greatly lowering the costs of adding such measurement to population-scale research. However, the field currently has no carefully studied protocol for large-scale hair collection, and no information about the selection biases likely to result from self-collection rather than professional-collection.

We will overcome this obstacle by using a large, random-assignment experiment to assess options for integration of hair-based cortisol measurement into population-scale studies. This experiment, comparing self-collection of hair for cortisol to professional-collection, will be integrated into a long-term family panel study with existing predictors of stress and the transition to adulthood from neighborhoods, households, parents, and individual young adults. These measures will support comprehensive evaluation of the selection bias in self-collection of hair samples. We will randomly assign 1,448 respondents age 18-21 to two arms of an experiment comparing self-collection of hair to professional-collection. Analyses will examine success collecting hair, the quality of the hair sample, and the participant?s self-evaluation of the process. We will link measures of these outcomes to thousands of existing measures of events over time in the individuals? own lives, their parents? lives, the lives of other household members, and the local community context. Analyses will feature exploration of all measures to identify any that are associated with refusal to participate, compliance with self-collection, quality of the hair samples, or self-reports of adverse responses to the hair-collection protocols.

Results from these analyses will provide the means to establish the limitations of large-scale hair-based cortisol self-collection. We will design an optimal protocol for integrating hair-based cortisol collection into population studies across settings and release that protocol to the public. We will also archive these innovative cortisol measures at ICPSR, allowing all researchers to launch innovative new analyses of psychological stress in the transition to adulthood. At the conclusion of this R21, our team will propose R01-scale research using this new protocol to link mental health before COVID-19 and stress during COVID-19 era transitions to adulthood to trajectories of courtship, marriage, contraceptive use, and childbearing.