Area Under the Curve and Other Summary Indicators of Repeated Waking Cortisol Measurements

• Activity Number: 209
• Type: Contributed
• Date/Time: Monday, July 30, 2007 : 2:00 PM to 3:50 PM
• Sponsor: Section on Statistics in Epidemiology
• Author(s): Desta Fekedulegn*+ and Michael Andrew and Cecil M. Burchfiel and John M. Violanti and Tara A. Hartley and Luenda E. Charles and Diane B. Miller
• Companies: National Institute for Occupational Safety and Health and Centers for Disease Control and Prevention and National Institute for Occupational Safety and Health and State University of New York at Buffalo and National Institute for Occupational Safety and Health and National Institute for Occupational Safety and Health and National Institute for Occupational Safety and Health
• Keywords: Repeated cortisol measurements ; Area under the curve ; principal component analysis ; Total hormonal secretion ; Time course of salivary cortisol

Abstract

In research designed to assess health consequences of stress, repeated measurements of salivary cortisol are often used as a physiologic indicator of the responsiveness of the hypothalamic-pituitary-adrenal axis. There is a need to derive two forms of area under the curve that summarize the repeated measurements: AUCG and AUCI. In this study interpretation and generic definition of the area under the curve was provided through graphical analyses and examination of its association with other summary measures. In generic form AUCI is the area under the curve above the baseline value minus the area above the curve below the baseline value. The sign and magnitude of the parameter are related to the profile and the rate of change of the measurements over time. Principal components analyses revealed two groups of summary measures: measures of magnitude of response and pattern of response.