Example of Misclassification Bias

Pertussis Vaccine - 100% Specificity

Lead Author(s): Jeff Martin, MD

Misclassfication Bias

In a cohort study we have a special case of non-differential misclassification of outcome. In these special cases, if there is 100% specificity, there is no penalty for imperfect sensitivity. The following example of the pertussis vaccine will clarify this situation.

Pertussis Vaccine Efficacy

Ward studied the use of a pertussis vaccine in adults.


One of the outcomes looked at was clinical disease defined as cough of 5 or more days of duration. When the authors looked at a different outcome, cough plus microbiologic confirmation of pertussis, there were only 10 total events. What happened here: cough alone is a very non-specific way to capture pertussis.

Data on Outcomes


To summarize in this study, the efficacy of the pertussis vaccine was studied using two outcomes.


Ward, J. I., Cherry, J. D., Chang, S. J., Partridge, S., Lee, H., Treanor, J., et al. (2005). Efficacy of an acellular pertussis vaccine among adolescents and adults. N Engl J Med, 353 (15), 1555-156