In a case-control study of the relationship of radiation exposure and thyroid ca
ID: 3044436 • Letter: I
Question
In a case-control study of the relationship of radiation exposure and thyroid cancer, 50 cases admitted for thyroid cancer and 100 “controls” admitted during the same period for treatment of hernias were studied. Only the cases were interviewed, and 20 of the cases were found to have been exposed to x-ray therapy in the past, based on the interviews and medical records. The controls were not interviewed, but a review of their hospital records when they were admitted for hernia surgery revealed that only 2 controls had been exposed to x-ray therapy in the past.
1.Based on the description given above, what source of bias is least likely to be present in this study? [ONE POINT]
Recall bias
Bias due to loss of subjects from the control group over time
Bias due to controls being non-representative of the non-diseased population
Bias due to use of different methods of ascertainment of exposure in the cases and controls
Selection bias for exposure to x-ray therapy in the past
Explanation / Answer
Bias due to use of different methods of ascertainment of exposure in cases and controls might be the least likely source of bias present in the given study, since medical records reveal the actual data in most of the cases, for which the interview may be just a supporting statement.