Tags:
create new tag
, view all tags, tagging instructions

# Example of Misclassification Bias

## Non-Differential Exposure - Imperfect Sensitivity

Measurement bias is affected by imperfect sensitivity of exposure variables.

## Imperfect Sensitivity of Exposure Variables

In the diagram above the source population is on the top left and our study sample is on the bottom right.
• We use our study sample to make inferences about the source population.

## Study - Alcohol Abuse

Consider as an example of a case-control study of some disease and the exposure under study is alcohol abuse.
• Let's consider that among all true alcohol abusers our measurement, which is self-report, is only able to identify some fraction.
• In other words, we aren't able to get some alcohol abusers to admit that they are abusers.
• Hence, our measurement of alcohol use is insensitive. We depict this by showing an arrow going from the exposure cell to the unexposed cell.
• This is lack of complete sensitivity; in other words, we are misclassifying some alcohol users as non-users.

## Misclassification of Exposure

• This is called misclassification of exposure.
• Because the misclassification of exposure is occurring equally among the cases and controls, we call this non-differential with respect to disease.

## Non-Differential Misclassification of Exposure

• Overall, this is called non-differential misclassification of exposure.
Again, some truly exposed persons are misclassified as unexposed.
• Because this happens equally among diseased and non-diseased persons, it is called non-differential misclassification.

## Imperfect Sensitivity - Bias the OR towards the Null Hypothesis

In the top panel above is the truth where there is no misclassification of exposure -

What happens in the presence of 70% sensitivity in exposure classification?
• That means that 30% of truly exposed cases or 15 of 50 are instead classified as unexposed.
• Also, 30% of the 20 exposed controls are falsely classified as unexposed, or 6 persons.
• The bottom panel therefore shows what happens and you can see that the OR is now attenuated to 3.3.

## Bias Towards the Null Hypothesis

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

Topic revision: r6 - 03 Feb 2012 - 17:10:58 - PeterBacchetti

Copyright &© by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding CTSPedia? Send feedback