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Question 5#

A prospective cohort study was performed to determine the relative risk of radiation exposure on squamous cell carcinoma (SCC) of the skin in elderly Caucasian men. The results showed that radiation exposure increased the risk of cutaneous SCC with a relative risk of 0.76 and p-value of 0.035.

Which of the following is a serious limitation of this study?

A. Internal validity
B. External validity
C. Reliability
D. Measurement bias

Correct Answer is B


External validity. External validity, also known as generalizability, is the applicability of the results of the study to other populations. In other words, it extends the results beyond the cohort being studied. In this study, the external validity is clearly limited (restricted to elderly Caucasian men). (A) Internal validity is the validity of the study within the cohort itself. (C) Reliability is synonymous with reproducibility and precision and is defined as the degree to which repeated measurements under unchanged conditions show the same results. (D) Measurement bias is not the best answer because there is no information in this question related to the how the study was actually designed and conducted.