Bias in Epidemiologic Research

For the following study descriptions, describe potential bias (es) most likely to be present. Indicate how differential bias would affect the measure of association (would it be underestimated, overestimated or unchanged):

1. A cohort study was designed to look at the association of pesticides and the occurrence of childhood leukemia. Children living in rural areas were followed and leukemia rates were compared between those children living in areas with high and low pesticide exposure. Pesticide exposure was considered high if it was over 20 “units” and low if it was under 20 “units”.

Read more...