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Intralaboratory and Interlaboratory Relative Errors in Fiber Count by NIOSH 7400

by Stepan Reut

There ia a special attention to PCM fiber count method NIOSH 7400 in USA. Mostly because it is a part of the federal law and therefore it must be followed to the letter. Among any other requirements there is one which is really hard to follow: The final report should include intralaboratory and interlabortory relative erros (Sr).

Intralaboratory and intrelaboratory errors represent very different processes and if not used correctly can seriously bias interpretation of the lab results.

Intralaboratory error is a measure of laboratory accuracy and is specific to a particular laboratory. The typical Sr’s we see are between 0.15 and 0.30

Interlaboratory error is a property of the proficiency testing program and is a combination of the method error, the averaged error of all laboratories participating in the study, and variability of the test samples distributed between the labs for testing. The typical value is about Sr=0.45

In order to avoid confusions, the interlaboratory error is not reported.  

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