title: Attrition bias in a U.S. Internet survey of alcohol use among college freshmen.
abstract: OBJECTIVE
  Attrition bias is an important issue in survey research on alcohol, tobacco, and other drug use. The issue is even more salient for Internet studies, because these studies often have higher rates of attrition than face-to-face or telephone surveys, and there is limited research examining the issue in the field of drug usage, specifically for college underclassmen. This study assessed whether measures of high-risk drinking and alcohol-related consequences were related to attrition groups ("stayers" or "leavers") in a cohort of college freshmen.
  
  
  METHODS
  Data were collected in 2003 and 2004 from 2,144 first-year college students at 10 universities in the southeastern United States. Demographics, indicators of high-risk drinking, and alcohol-related consequences were compared between cohort stayers and leavers in statistical analyses using two methods.
  
  
  RESULTS
  Analyses indicated that cohort leavers reported significantly higher levels of high-risk drinking (past-30-day heavy episodic drinking, weekly drunkenness) and past-30-day smoking but not significantly increased alcohol-related consequences. The directionality of bias was modestly consistent across outcomes and comparison methods.
  
  
  CONCLUSIONS
  The current study's findings suggest that intervention efforts to reduce smoking or high-risk drinking need to consider attrition bias during study follow-up or account for it in analyses.
authors.affiliation: Department of Biostatistical Sciences, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA. tmccoy@wfubmc.edu
authors.forename: Thomas P
authors.initials: TP
authors.lastname: McCoy
authors.forename: Edward H
authors.initials: EH
authors.lastname: Ip
authors.forename: Jill N
authors.initials: JN
authors.lastname: Blocker
authors.forename: Heather
authors.initials: H
authors.lastname: Champion
authors.forename: Scott D
authors.initials: SD
authors.lastname: Rhodes
authors.forename: Kimberly G
authors.initials: KG
authors.lastname: Wagoner
authors.forename: Ananda
authors.initials: A
authors.lastname: Mitra
authors.forename: Mark
authors.initials: M
authors.lastname: Wolfson
mesh_terms: D000293:Adolescent; D000428:Alcohol Drinking / Q000009:adverse effects / Q000453:epidemiology*; D019973:Alcohol-Related Disorders / Q000453:epidemiology; D003625:Data Collection / Q000379:methods*; D005260:Female; D006801:Humans; D020407:Internet; D008297:Male; D010352:Patient Dropouts; D015983:Selection Bias; D012907:Smoking; D013334:Students / Q000523:psychology*; D014481:United States / Q000453:epidemiology