In prospective cohort studies, why is loss to follow‐up a source of selection bias?
A)The study will no longer be representative of the general population
B)It reduces the size of the study sample
C)Those lost to follow‐up may have different characteristics to those who remain in the study
D)Those who are lost to follow‐up may recall things differently from those who remain in the study
E)There is more likely to be ascertainment bias when measuring outcomes in those who remain in the study

Question

Quizplus · Accepted Answer

Those lost to follow‐up may have different characteristics to those who
remain in the study.If these characteristics are related to disease outcomes, then this
differential selection out of the study will lead to biased effect estimates.Most cohort
studies are not directly representative of the general population anyway (A); the sample
will be smaller but this does not in itself introduce selection bias (B); recall bias is
irrelevant to follow‐up in a cohort study (D); and errors in outcome ascertainment
within the study will be unrelated to any losses of participants from it (E).

In Prospective Cohort Studies, Why Is Loss to Follow‐up a Source