Example of Misclassification Bias

Non-Differential Misclassification of Outcome

Lead Author(s): Jeff Martin, MD

Misclassification of the outcome results in measurement bias.


When the degree of misclassification of outcome is the same in the exposed vs unexposed groups, i.e. independent of exposure, this is called non differential misclassification of outcome.

As shown in the diagram (2x2 table)below, the arrows in cells 2 and 4 depict diseased persons misclassified as non-diseased - in other words problems with sensitivity.

Figure - Imperfect Sensitivity and Specificity

The figure below from Copeland (1977) looks at the effects of imperfect specificity and sensitivity in the measurement of outcome.

The figure illustrates that you take a pretty big hit in the observed risk ratio with only subtle changes in specificity.

Also, there is not that much dependence on sensitivity.

Non-Differential Misclassification of Outcome: Effect of Incidence - Figure

In the figure below, Copeland (1977) shows the importance of the underlying frequency of the outcome, in other words, the cumulative incidence of outcome on the results.

Here are three scenarios of where the true risk ratio is 2.0. 0120_outcome3.JPG

Sensitivity Fixed - Changes in Specificity

The sensitivity of the outcome measurement is held fixed at a realistic 90% and the curves show you what happen as specificity falls. This dependence upon outcome incidence when talking about misclassification of outcome is akin to the situation of misclassification of exposure where there is a dependence upon overall prevalence of exposure.


Copeland, K. T., Checkoway, H., McMichael, A. J., & Holbrook, R. H. (1977). Bias due to misclassification in the estimation of relative risk. Am J Epidemiol, 105 (5), 488-495.