title: Quantifying the impact of selection bias caused by nonparticipation in a case-control study of mobile phone use.
abstract: OBJECTIVE
  To quantitatively assess the impact of selection bias caused by nonparticipation in a multinational case-control study of mobile phone use and brain tumor.
  
  
  METHODS
  Non-response questionnaires (NRQ) were completed by a sub-set of nonparticipants. Selection bias factors were calculated based on the prevalence of mobile phone use reported by nonparticipants with NRQ data, and on scenarios of hypothetical exposure prevalence for other nonparticipants.
  
  
  RESULTS
  Regular mobile phone use was reported less frequently by controls and cases who completed the NRQ (controls, 56%; cases, 50%) than by those who completed the full interview (controls, 69%; cases, 66%). This relationship was consistent across study centers, sex, and age groups. Lower education and more recent start of mobile phone use were associated with refusal to participate. Bias factors varied between 0.87 and 0.92 in the most plausible scenarios.
  
  
  CONCLUSIONS
  Refusal to participate in brain tumor case-control studies seems to be related to less prevalent use of mobile phones, and this could result in a downward bias of around 10% in odds ratios for regular mobile phone use. The use of simple selection bias estimation methods in case-control studies can give important insights into the extent of any bias, even when nonparticipant information is incomplete.
authors.affiliation: International Agency for Research on Cancer, Lyon, France. mvrijheid@creal.cat
authors.forename: Martine
authors.initials: M
authors.lastname: Vrijheid
authors.forename: Lesley
authors.initials: L
authors.lastname: Richardson
authors.forename: Bruce K
authors.initials: BK
authors.lastname: Armstrong
authors.forename: Anssi
authors.initials: A
authors.lastname: Auvinen
authors.forename: Gabriele
authors.initials: G
authors.lastname: Berg
authors.forename: Matthew
authors.initials: M
authors.lastname: Carroll
authors.forename: Angela
authors.initials: A
authors.lastname: Chetrit
authors.forename: Isabelle
authors.initials: I
authors.lastname: Deltour
authors.forename: Maria
authors.initials: M
authors.lastname: Feychting
authors.forename: Graham G
authors.initials: GG
authors.lastname: Giles
authors.forename: Martine
authors.initials: M
authors.lastname: Hours
authors.forename: Ivano
authors.initials: I
authors.lastname: Iavarone
authors.forename: Susanna
authors.initials: S
authors.lastname: Lagorio
authors.forename: Stefan
authors.initials: S
authors.lastname: Lönn
authors.forename: Mary
authors.initials: M
authors.lastname: McBride
authors.forename: Marie-Elise
authors.initials: ME
authors.lastname: Parent
authors.forename: Siegal
authors.initials: S
authors.lastname: Sadetzki
authors.forename: Tina
authors.initials: T
authors.lastname: Salminen
authors.forename: Marie
authors.initials: M
authors.lastname: Sanchez
authors.forename: Birgitte
authors.initials: B
authors.lastname: Schlehofer
authors.forename: Joachim
authors.initials: J
authors.lastname: Schüz
authors.forename: Jack
authors.initials: J
authors.lastname: Siemiatycki
authors.forename: Tore
authors.initials: T
authors.lastname: Tynes
authors.forename: Alistair
authors.initials: A
authors.lastname: Woodward
authors.forename: Naohito
authors.initials: N
authors.lastname: Yamaguchi
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Cardis
mesh_terms: D000328:Adult; D000367:Age Factors; D001932:Brain Neoplasms / Q000453:epidemiology* / Q000209:etiology*; D016022:Case-Control Studies; D040421:Cell Phone / Q000706:statistics & numerical data*; D004522:Educational Status; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015983:Selection Bias; D012737:Sex Factors