Question

Suppose you conduct a case-control study of endometrial cancer, with 120 cases and 120 unmatched controls.  According to medical records (which we will assume are correct), 100 of the cases and 60 of the controls have used postmenopausal estrogens.

Suppose another researcher is not careful about reviewing the medical records, and overlooks the postmenopausal estrogen use for 20% of the exposed subjects in the above study, so that 20% of the exposed cases are counted as unexposed and 20% of the exposed controls are counted as unexposed.

(i) Reconstruct the 2x2 table to reflect this misclassification of exposure, and recompute the odds ratio for postmenopausal estrogen use vs endometrial cancer.

(ii) Why is this misclassification of exposure considered nondifferential?

(iii) In what direction is the bias that results from this nondifferential misclassification of exposure?

(iv) Is this the usual direction of bias from nondifferential misclassification?

Answer 1

​​​​​​Q1) Reconstruct the 2x2 table to reflect this misclassification of exposure, and recompute the odds ratio for postmenopausal estrogen use vs endometrial cancer?

Ans : 2*2 Table : SCENARIO -1

100 cases -----60 controls postmenopausal estrogen

60 cases -------20% unexposed cases (12 cases)

60 cases-------20% exposed cases (12 cases)

SCENARIO 2 -(According to 120)

120 Cases----- 24 (unexposed cases)

120 Cases----- 24 (exposed cases)

Q2) Why is this misclassification of exposure considered nondifferential?

Ans : This misclassification of exposure considered nondifferential because this misclassification has occurred and this error happened when information is incorrect, but it is the same across groups. It happens when exposure is unrelated to another variables, or when the disease is unrelated to other variables (including exposure).

Q3) In what direction is the bias that results from this nondifferential misclassification of exposure?

Ans : This non differential misclassification of exposure directs, as the another researcher not carefully review the records and postmenopausal estrogen was overlooked and exposed patients were unexposed and unexposed were exposed.

Q4) Is this the usual direction of bias from nondifferential misclassification?

Ans : Usual direction of bias is not definitely determined because nondifferential misclassification occurs usually within the same group only information is incorrect.