title: Regression to the mean and changes in risk behavior following study enrollment in a cohort of U.S. women at risk for HIV.
abstract: OBJECTIVE
  Reductions in risk behaviors are common following enrollment in human immunodeficiency virus (HIV) prevention studies. We develop methods to quantify the proportion of change in risk behaviors that can be attributed to regression to the mean versus study participation and other factors.
  
  
  METHODS
  A novel model that incorporates both regression to the mean and study participation effects is developed for binary measures. The model is used to estimate the proportion of change in the prevalence of "unprotected sex in the past 6 months" that can be attributed to study participation versus regression to the mean in a longitudinal cohort of women at risk for HIV infection who were recruited from ten U.S. communities with high rates of HIV and poverty. HIV risk behaviors were evaluated using audio computer-assisted self-interviews at baseline and every 6 months for up to 12 months.
  
  
  RESULTS
  The prevalence of "unprotected sex in the past 6 months" declined from 96% at baseline to 77% at 12 months. However, this change could be almost completely explained by regression to the mean.
  
  
  CONCLUSIONS
  Analyses that examine changes over time in cohorts selected for high- or low- risk behaviors should account for regression to the mean effects.
authors.affiliation: Department of Biostatistics, University of Washington, Seattle, WA; Fred Hutchinson Cancer Research Center, Seattle, WA. Electronic address: jphughes@uw.edu.
authors.forename: James P
authors.initials: JP
authors.lastname: Hughes
authors.affiliation: Department of Behavioral Sciences and Health Education, Emory University Rollins School of Public Health, Atlanta, GA; Family Health International-FHI360, Durham, NC.
authors.forename: Danielle F
authors.initials: DF
authors.lastname: Haley
authors.affiliation: Department of Behavioral Sciences and Health Education, Emory University Rollins School of Public Health, Atlanta, GA; Department of Medicine, Division of Infectious Diseases, Emory University School of Medicine, Atlanta, GA.
authors.forename: Paula M
authors.initials: PM
authors.lastname: Frew
authors.affiliation: School of Medicine, University of North Carolina, Chapel Hill, NC; Gillings School of Public Health, University of North Carolina, Chapel Hill, NC.
authors.forename: Carol E
authors.initials: CE
authors.lastname: Golin
authors.affiliation: School of Medicine, University of North Carolina, Chapel Hill, NC; Gillings School of Public Health, University of North Carolina, Chapel Hill, NC.
authors.forename: Adaora A
authors.initials: AA
authors.lastname: Adimora
authors.affiliation: Department of Epidemiology and Biostatistics, George Washington University, Washington, DC.
authors.forename: Irene
authors.initials: I
authors.lastname: Kuo
authors.affiliation: Departments of Epidemiology and Medicine, ICAP at Columbia, Columbia University, New York, NY.
authors.forename: Jessica
authors.initials: J
authors.lastname: Justman
authors.affiliation: National Institute of Allergy and Infectious Diseases, Bethesda, MD.
authors.forename: Lydia
authors.initials: L
authors.lastname: Soto-Torres
authors.affiliation: Fred Hutchinson Cancer Research Center, Seattle, WA.
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
authors.affiliation: West Virginia University Clinical and Translational Science Institute, Morgantown, WV.
authors.forename: Sally
authors.initials: S
authors.lastname: Hodder
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D015658:HIV Infections / Q000453:epidemiology*; D006801:Humans; D008137:Longitudinal Studies; D015233:Models, Statistical; D012044:Regression Analysis; D012309:Risk-Taking; D014481:United States / Q000453:epidemiology; D047568:Unsafe Sex / Q000706:statistics & numerical data*; D055815:Young Adult
keywords: HIV; Logistic regression; Risk behavior; Statistical model