title: Comparison of the sociodemographic characteristics of the large NutriNet-Santé e-cohort with French Census data: the issue of volunteer bias revisited.
abstract: BACKGROUND
  A recurring concern in traditional and in Web-based studies pertains to non-representativeness due to volunteer bias. We investigated this issue in an ongoing, large population-based e-cohort.
  
  
  METHODS
  The sample included 122 912 individuals enrolled in the Internet-based, nutrition-focused NutriNet-Santé study between May 2009 and March 2014, with complete baseline data. Participants were recruited via recurrent multimedia campaigns and other traditional and online strategies. Individuals aged 18+ years, residing in France and having Internet access, were eligible for enrolment. Their sociodemographic characteristics were compared with the corresponding 2009 Census data via χ(2) goodness-of-fit tests. The effectiveness of statistical weighting of the e-cohort data was also explored.
  
  
  RESULTS
  The sample exhibited marked geographical and sociodemographic diversity, including volunteers belonging to typically under-represented subgroups in traditional surveys (unemployed, immigrants, the elderly). Nonetheless, the proportions of women, relatively well-educated individuals and those who are married or cohabiting, were notably larger compared with the corresponding national figures (women: 78.0% vs 52.4%; postsecondary education: 61.5% vs 24.9%; married or cohabiting: 70.8% vs 62.0%, respectively; all p<0.0001).
  
  
  CONCLUSIONS
  There were notable sociodemographic differences between the general French population and this general population-based e-cohort, some of which were corrected by statistical weighting. The findings bear on the potential generalisability of future investigations in the context of e-epidemiology.
authors.affiliation: Université Paris 13, Equipe de Recherche en Epidémiologie Nutritionnelle (EREN), Centre de Recherche en Epidémiologie et Statistiques, Inserm (U1153), Inra (U1125), Cnam, COMUE Sorbonne Paris Cité, Bobigny, France.
authors.forename: Valentina A
authors.initials: VA
authors.lastname: Andreeva
authors.affiliation: Unité de Surveillance en Epidémiologie Nutritionnelle (USEN), Institut de Veille Sanitaire, Université Paris 13, Centre d'Epidémiologie et Biostatistiques, Sorbonne Paris Cité, Bobigny, France.
authors.forename: Benoît
authors.initials: B
authors.lastname: Salanave
authors.affiliation: Unité de Surveillance en Epidémiologie Nutritionnelle (USEN), Institut de Veille Sanitaire, Université Paris 13, Centre d'Epidémiologie et Biostatistiques, Sorbonne Paris Cité, Bobigny, France.
authors.forename: Katia
authors.initials: K
authors.lastname: Castetbon
authors.affiliation: Unité de Surveillance en Epidémiologie Nutritionnelle (USEN), Institut de Veille Sanitaire, Université Paris 13, Centre d'Epidémiologie et Biostatistiques, Sorbonne Paris Cité, Bobigny, France.
authors.forename: Valérie
authors.initials: V
authors.lastname: Deschamps
authors.affiliation: Unité de Surveillance en Epidémiologie Nutritionnelle (USEN), Institut de Veille Sanitaire, Université Paris 13, Centre d'Epidémiologie et Biostatistiques, Sorbonne Paris Cité, Bobigny, France.
authors.forename: Michel
authors.initials: M
authors.lastname: Vernay
authors.affiliation: Université Paris 13, Equipe de Recherche en Epidémiologie Nutritionnelle (EREN), Centre de Recherche en Epidémiologie et Statistiques, Inserm (U1153), Inra (U1125), Cnam, COMUE Sorbonne Paris Cité, Bobigny, France.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Kesse-Guyot
authors.affiliation: Université Paris 13, Equipe de Recherche en Epidémiologie Nutritionnelle (EREN), Centre de Recherche en Epidémiologie et Statistiques, Inserm (U1153), Inra (U1125), Cnam, COMUE Sorbonne Paris Cité, Bobigny, France Unité de Surveillance en Epidémiologie Nutritionnelle (USEN), Institut de Veille Sanitaire, Université Paris 13, Centre d'Epidémiologie et Biostatistiques, Sorbonne Paris Cité, Bobigny, France Département de Santé Publique, Hôpital Avicenne, Bobigny, France.
authors.forename: Serge
authors.initials: S
authors.lastname: Hercberg
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015982:Bias; D019352:Censuses; D015331:Cohort Studies; D005260:Female; D005602:France; D006801:Humans; D020407:Internet; D008297:Male; D008875:Middle Aged; D009749:Nutrition Surveys / Q000379:methods / Q000592:standards*; D014838:Volunteers; D055815:Young Adult
keywords: Cohort studies; Epidemiological methods; RESEARCH METHODS; Research Design in Epidemiology