Example of Misclassification Bias

Non-Differential Exposure - Cohort Study

Lead Author(s): Jeff Martin, MD

Figure - Misclassification of Exposure Variable

Flegal (1986) plots the effect of non-differential misclassification of exposure in a cohort study.


Discussion of Figure

The figure points out a few things:

1. Even with these seemingly reassuring combinations of sensitivity and specificity, the highest risk ratio we can get is 8 or a 20% decline.

2. For most overall prevalences of exposure, say from .25 and higher, you see a bigger influence of sensitivity than specificity. 3. Illustrating the important dependence of the prevalence of the exposure. As you get to the extremes of imbalance between exposed and unexposed, you see that the apparent (or observed) risk ratio starts to plummet.

Is it theoretically possible to have differential misclassification of exposure in a cohort study? No, because at the beginning of a cohort when measurements of exposure are made the outcome has not yet occurred.


Flegal, K. M., Brownie, C., & Haas, J. D. (1986). The effects of exposure misclassification on estimates of relative risk. Am J Epidemiol, 123 (4), 736-751.