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Published on: April 30, 2020
Selection bias due to differential participation in a case-control study of mobile phone use and brain tumors
Anna Lahkola1, Tiina Salminen, Anssi Auvinen
1STUK-Radiation and Nuclear Safety Authority, FIN-00881 Helsinki, Finland. anna.lahkola@stuk.fi
Purpose:
To evaluate the possible selection bias related to the differential participation of mobile phone users and non-users in a Finnish case-control study on mobile phone use and brain tumors.
Methods:
Mobile phone use was investigated among 777 controls and 726 cases participating in the full personal interview (full participants), and 321 controls and 103 cases giving only a brief phone interview (incomplete participants). To assess selection bias, the Mantel-Haenszel estimate of odds ratio was calculated for three different groups: full study participants, incomplete participants, and a combined group consisting of both full and incomplete participants.
Results:
Among controls, 83% of the full participants and 73% of the incomplete participants had regularly used a mobile phone. Among cases, the figures were 76% and 64%, respectively. The odds ratio for brain tumor based on the combined group of full and incomplete participants was slightly closer to unity than that based only on the full participants.
Conclusions:
Selection bias tends to distort the effect estimates below unity, while analyses based on more comprehensive material gave results close to unity.
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