title: Need for informed consent in substance use studies--harm of bias?
abstract: OBJECTIVE
  The aim of this study was to examine the differences between those who gave informed consent to a study on substance use and those who did not, and to analyze whether differences changed with varying nonconsent rates.
  
  
  METHODS
  Cross-sectional questionnaire data on demographics, alcohol, smoking, and cannabis use were obtained for 6,099 French- and 5,720 German-speaking 20-year-old Swiss men. Enrollment took place over 11 months for the Cohort Study on Substance Use Risk Factors (C-SURF). Consenters and nonconsenters were asked to complete a short questionnaire. Data for nearly the entire population were available because 94% responded. Weekly differences in consent rates were analyzed. Regressions examined the associations of substance use with consent giving and consent rates and the interaction between the two.
  
  
  RESULTS
  Nonconsenters had higher substance use patterns, although they were more often alcohol abstainers; differences were small and not always significant and did not decrease as consent rates increased.
  
  
  CONCLUSIONS
  Substance use currently is a minor sensitive topic among young men, resulting in small differences between nonconsenters and consenters. As consent rates increase, additional individuals are similar to those observed at lower consent rates. Estimates of analytical studies looking at associations of substance use with other variables will not differ at reasonable consent rates of 50%-80%. Descriptive prevalence studies may be biased, but only at very low rates of consent.
authors.affiliation: Alcohol Treatment Centre, Lausanne University Hospital CHUV, Lausanne, Switzerland.
authors.forename: Joseph
authors.initials: J
authors.lastname: Studer
authors.forename: Meichun
authors.initials: M
authors.lastname: Mohler-Kuo
authors.forename: Petra
authors.initials: P
authors.lastname: Dermota
authors.forename: Jacques
authors.initials: J
authors.lastname: Gaume
authors.forename: Nicolas
authors.initials: N
authors.lastname: Bertholet
authors.forename: Charlotte
authors.initials: C
authors.lastname: Eidenbenz
authors.forename: Jean-Bernard
authors.initials: JB
authors.lastname: Daeppen
authors.forename: Gerhard
authors.initials: G
authors.lastname: Gmel
mesh_terms: D000428:Alcohol Drinking / Q000523:psychology; D015982:Bias; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D006801:Humans; D007258:Informed Consent; D008297:Male; D008385:Marijuana Smoking / Q000523:psychology; D012044:Regression Analysis; D012107:Research Design; D012307:Risk Factors; D012907:Smoking / Q000523:psychology; D019966:Substance-Related Disorders / Q000523:psychology*; D011795:Surveys and Questionnaires; D013557:Switzerland; D055815:Young Adult