Example of Misclassification Bias

Non-Differential Exposure - Imperfect Specificity

Lead Author(s): Jeff Martin, MD

Measurement bias results from imperfect specificity of the exposure variable.

Imperfect Specificity


In the diagram above the source population is on the top left and our study sample is on the bottom right.

Study - Second Hand Cigarette Smoke

The above schematic representation of misclassification of exposure when we have imperfect specificity. Persons who are truly unexposed but who are classified as exposed (because of faulty self-report) are reflected in both arrows. This is happening to the same degree in the diseased individuals as it is in the non-diseased individuals.

Non-Differential Misclassification of Exposure

Imperfect Specificity - Bias the OR towards the Null Hypothesis


Here is what non-differential misclassification of exposure because of problems of specificity would look like numerically. What happens in the presence of 70% specificity in exposure classification?

Bias Towards the Null Hypothesis

This illustrates the effect of non-differential misclassification of exposure because of imperfect specificity in the presence of 2 exposure categories -