In a case-control study of beta carotene and risk of lung cancer, serum specimen

Question

In a case-control study of beta carotene and risk of lung cancer, serum specimens frozen and stored 20 years earlier are compared between cases and controls. Later it is found that the freezer containing samples from cancer patients was defective, causing deterioration of the samples and making it difficult to measure the levels of beta-carotene. Which of the following sources of bias did the deterioration cause? Selection bias Non-differential misclassification Differential misclassification None of the above

Explanation / Answer

The correct answer would be: selection bias

Reason: As the sample were deteriorated, the samples would not help to investogate the level of beta carotene in the cases(the ones with lung cancer) that we wanted to investigate and compare with the control.

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