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?