Researchers used a matched case-control study design to investigate whether mobile phone use was associated with the development of glioma, a malignancy of the central nervous system.1 Cases and controls were matched for age and sex. Information about potential risk factors was collected using a self report questionnaire.

Which of the following statements, if any, are true?

• a) Matching reduces assessment bias of the potential risk factors

• b) Matching adjusts for the effects of age and sex as confounding variables

• c) Matching eliminates allocation bias

• d) Matching reduces recall bias