Card 11 / 13: This question is based on the following article: Handheld Cellular Telephone Use and Risk of Brain Cancer. JAMA: 2000 Dec; 284(23):3001 -3007. In this study, 469 men and women with brain cancer aged 18-80 years from participating hospitals were matched to 422 controls from those same hospitals. The investigators subsequently compared their past and current use of cellular telephones. After adjusting for confounders, the odds ratio comparing those who never used cellular telephones with past or present users was 0.85 (95% CI: 0.6-1.2). From the information above, which of the following are correct? (Select all that apply.)
A) This type of study is efficient in comparing rare outcomes.
B) One of the goals of choosing controls from the same hospitals as the cases in this study was to avoid selection bias.
C) The internal validity of the study would have been improved if the controls were selected from the general population.
D) In general, this type of study is prone to selection bias, because it is retrospective, and outcome status has already been established at the beginning of the study.

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