A case-control study was conducted to assess whether occupational radiation exposure among men was associated with Down syndrome in their children. The investigators matched cases and controls on age of the mother at childbirth by 5-year categories.
1. When possible, information on paternal radiation exposure was taken from employment records rather than from subject interviews. Why was this done?
O To minimize recall bias of exposure
O To minimize detection bias for cases
O To minimize differential misclassification of exposure
O To remove selection bias of non-radiation exposed fathers
O To provide dose-response information

Option A, To minimize recall bias of exposure

Explanation:

In a case control study, two group as are studied and compared on the basis of some supposed causal attribute

In this case the supposed causal attribute is association of down syndrome in children with the occupational radiation exposure of their fathers.  

If the parents are interviewed about their history of occupational radiation exposure, there are high chances of them making mistakes while recalling.  

Hence, instead of interview paternal radiation exposure was taken from employment records

Hence, option A is correct

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.