Posted: October 3rd, 2016

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.

15. Residents of three villages with three different types of water supply were asked to participate in a survey to identify cholera carriers. Because several cholera deaths had occurred recently, virtually everyone present at the time underwent examination. The proportion of residents in each village who were carriers was computed and compared. What is the proper classification for this study? [ONE POINT]
a. Case-control study
b. Concurrent cohort study
c. Non-concurrent cohort study
d. Cross-sectional study
e. Experimental study

Question 16 is based on the information given below:

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.
16. Based on the description given above, what source of bias is least likely to be present in this study? [ONE POINT]
a. Recall bias
b. Bias due to loss of subjects from the control group over time
c. Bias due to controls being non-representative of the non-diseased population
d. Bias due to use of different methods of ascertainment of exposure in cases and controls
e. Selection bias for exposure to x-ray therapy in the past