GUM (Guide to the Expression of Uncertainty in Measurement) for laboratories (and manufacturers) is what CLSI C51 is all about. (GUM was originally used to provide information about reference materials). I have previously commented that I didn’t think that GUM was a good idea for laboratories (1). I was also initially on the C51 subcommittee but since I couldn’t convince anyone about my point of view, I bailed.
To recall some of the problems with GUM …
- bias is not allowed – it must be corrected. But you could ignore big, rare biases (outliers) as well as real small biases.
- To obtain the standard deviations or bias corrections applied by manufacturers was impractical if not impossible for laboratories as in … Let’s set up a fixture and measure the variability of 10 pumps we just bought for this experiment.
- The math required to put together an estimate will make most people’s head spin.
In the C51 version of GUM, there is only 1 example – that of measuring a bunch of controls. This is not GUM! and will not provide an uncertainty estimate for patient samples since controls do not estimate the non specificity assay errors in patient samples.
- Krouwer JS A Critique of the GUM Method of Estimating and Reporting Uncertainty in Diagnostic Assays Clin Chem 2003;49:1818-1821.