In the standard ISO 13528:2015 to be considered for the evaluation of laboratory proficiency testing, 11 is proposed as the minimum number of participants in laboratory proficiency testing. If then the inter-laboratory variation (standard deviation) calculated during evaluation and the target standard deviation used for the evaluation of the results are about the same, the influence of the uncertainty of the reference value is acceptable: The value of the uncertainty (in z-scores) then corresponds to 0.3 z-score, which, starting from an "action level z-score 3", corresponds to 10 %.
LVU mainly offers proficiency tests where several parameters can be examined. Experience has shown that not all participants submit results or process all parameters, so in actual practise a higher minimum number of participants than 11 is required in order to enable an evaluation of the parameters. For this reason, LVU will only carry out proficiency tests if an evaluation will be possible on the basis of the registrations received.