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.
- selection bias
- socioeconomic factors
- cancer epidemiology
- case control me
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Funding This work was supported by the European Union Fifth Framework Program, ‘Quality of Life and Management of living Resources’ (contract QLK4-CT-1999-01563), International Union against Cancer (UICC), the Swedish Research Council, and the Swedish Cancer Society. The UICC received funds for this purpose from the Mobile Manufacturers' Forum and GSM Association. Provision of funds to the INTERPHONE study investigators via the UICC was governed by agreements that guaranteed INTERPHONE's complete scientific independence. These agreements are publicly available at http://www.iarc.fr/ENG/Units/RCAd.html.
Competing interests None.
Ethics approval The study was approved by the ethics committee at Karolinska Institutet in Stockholm.
Provenance and peer review Not commissioned; externally peer reviewed.