How is the bias calculated?

The bias is simply the difference between your result and the mean value, represented as a percentage. It should be noted, however, that the bias of specialist labs will be calculated from the RTAC mean, whilst the non-RTAC labs have the bias calculated from the overall ALTM. The formula is as follows:

Bias = ([x - ø]/ø) × 100

where: x = your result
ø = mean value (RTAC or ALTM)