Ascertainment bias: A feasible form of bias, particularly in the retrospective studies, which arises from the relationship between the exposure to the risk factor and the probability of detecting an event of interest. In the research comparing women with cervical cancer and the control group, for instance, an excess of oral contraceptive use with the cases might possibly be due to more often screening for the disease among the women known to be taking the pill.

A diagram illustrating the feed-forward network.