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Study Bias for Case-Control Study

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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 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.

Based on the description given above, what source of bias is least likely to be present in this study?? Answer is: Bias due to loss of subjects from the control group over time. But why is this the correct answer?? Review questions did not give rationale in the textbook. Thank you...

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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 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.

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Usually, when you are doing a longitudinal research study, one major bias results when you loose participants all through the study. People could drop out, move, no longer want to be part of the ...

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