title: Intraindividual variability in cortisol: Approaches, illustrations, and recommendations.
abstract: Most of the variance in diurnal cortisol is attributable to intraindividual variability (IIV), defined as relatively short-term, reversible changes. Multiple methods for measuring IIV have been proposed, and some have already been applied to cortisol IIV. In the present review, measurement methods are described and applied to simulated cortisol data with known underlying differences in IIV and to real cortisol data from first-year law students. More slope variance and more residual or net variance were well captured by their individual standard deviations. Explorations of reliability suggested that 10 slopes and 50 residuals result in reliable and stable estimates of the individual standard deviations. A data-analytic plan for cortisol IIV is provided.
authors.affiliation: Department of Psychology, University of Kentucky, 125 Kastle Hall, Lexington, KY 40506-0044, United States. Electronic address: segerstrom@uky.edu.
authors.forename: Suzanne C
authors.initials: SC
authors.lastname: Segerstrom
authors.affiliation: Department of Psychological and Brain Sciences, University of Louisville,317 Life Sciences Building, Louisville, KY 40292, United States. Electronic address: sephton@louisville.edu.
authors.forename: Sandra E
authors.initials: SE
authors.lastname: Sephton
authors.affiliation: Department of Biostatistics, University of Kentucky,111 Washington Avenue, Lexington, KY 40536, United States. Electronic address: philip.westgate@uky.edu.
authors.forename: Philip M
authors.initials: PM
authors.lastname: Westgate
mesh_terms: D006801:Humans; D006854:Hydrocortisone / Q000032:analysis*; D007206:Individuality; D015203:Reproducibility of Results
chemical_list: D006854:Hydrocortisone
keywords: Autocorrelation; Cortisol; Intraindividual variability; Reliability; Root mean squared successive difference; Standard deviation