This occurred in only a small number of places, and was corrected where clear misclassification had occurred.
If any misclassification had occurred, it would have been in both groups and of a non-differential nature.
However, all hazard ratios for train drivers were close to 1 and an important risk increase could only have been missed if major outcome misclassification had occurred, which is unlikely.
Secondly, as in many other studies, CAP uses the endpoint committee for final UCD assignment but have no means of ascertaining if any misclassifications have occurred at this level.
With a strict definition of AMI, it is unlikely that misclassification of AMI has occurred, which would unduly bias VE calculations.
One can use the method of analysis for effect estimation with many study designs when error in measurement or misclassification of independent variables has occurred.
1, 6, 7, 10 Assuming that misclassification may have occurred, the impact of such misclassification seems minor, since outcome endpoints for the different N classes showed a similar pattern irrespective of the frequency of LNMM in the hospitals.
The principal weakness of our study is the use of a Job Exposure Matrices (JEMs) that can lead to non-differential misclassification of exposure [ 22], and we would expect non-differential misclassification to have occurred.
Fourth, since this retrospective study used ICD-9 coding, patient misclassification could have occurred and led to under- or over-reporting.
