title: Non-participant characteristics and the association between socioeconomic factors and brain tumour risk.
abstract: BACKGROUND
  The aim of the study was to identify demographic and socioeconomic characteristics of participants and non-participants in a Swedish population-based case-control study on brain tumours and to analyse the association between socioeconomic factors and glioma and meningioma risk.
  
  
  METHODS
  Record linkage was made to an official register to gather information on socioeconomic status, income, education and demography for all participating and non-participating cases and controls.
  
  
  RESULTS
  494 glioma cases, 321 meningioma cases and 955 controls were eligible and 74%, 85% and 70%, respectively, participated. Working status and income level were positively associated with participation among cases and controls. Among both cases and controls, being married, and having a high education were also associated with participation. Having a family income level in the highest quartile was associated with an increased glioma risk (OR 1.5, 95% CI 1.1 to 2.1). This risk increase diminished when only participating individuals were included in the analysis. Socioeconomic factors were not associated with meningioma risk.
  
  
  CONCLUSIONS
  Non-participation, related to socioeconomic factors, is a potential source of bias in case-control studies that should be acknowledged; however, the effect was not large in the present study due to the fact that the level of participation was comparable between cases and controls and participation was similarly influenced by socioeconomic factors among cases and controls. The association between a high income level and an increased glioma risk and possible underlying factors needs to be explored further.
authors.affiliation: Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden. annette.wigertz@ki.se
authors.forename: Annette
authors.initials: A
authors.lastname: Wigertz
authors.forename: Stefan
authors.initials: S
authors.lastname: Lönn
authors.forename: Per
authors.initials: P
authors.lastname: Hall
authors.forename: Maria
authors.initials: M
authors.lastname: Feychting
mesh_terms: D000328:Adult; D000368:Aged; D015982:Bias; D001932:Brain Neoplasms / Q000191:economics* / Q000453:epidemiology; D016022:Case-Control Studies; D004522:Educational Status; D004651:Employment; D005260:Female; D005910:Glioma / Q000191:economics* / Q000453:epidemiology; D006801:Humans; D007182:Income; D008297:Male; D008393:Marriage; D008577:Meningeal Neoplasms / Q000191:economics* / Q000453:epidemiology; D008579:Meningioma / Q000191:economics* / Q000453:epidemiology; D008875:Middle Aged; D012042:Registries / Q000706:statistics & numerical data; D012189:Retrospective Studies; D012923:Social Class; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult