On interchangeability of two laboratories

Abstract

This paper proposes a measure for assessing the equivalence between the results of two laboratories. The measure is called asymmetric interchangeability. It is asymmetric since, based on this measure, one laboratory may be considered interchangeable with another laboratory but the converse may not be true. Such a situation can arise when the accuracy and precision of one laboratory are noticeably greater than that of the other. The proposed measure of interchangeability depends on the parameters of the measurement models, which include means, variances and the correlation of the two laboratories being compared. Since the level of correlation is often difficult to assess, it is assumed to be zero in this paper. Fiducial procedures are presented for testing the hypothesis that a laboratory is directionally interchangeable with another. The procedure is based on comparing a probability measure, which is shown to be closely related to asymmetric interchangeability, with an agreed threshold. Computer programs for calculating the p-value of the tests, written by use of open-source software, are listed.

Assessing compatibility of two laboratories: formulations as a statistical hypothesis testing problem

“…The situation does not change for the better when the null hypothesis is that of non-conformity as the power function remains small on the alternative. The power function of the test of |µ 1 − µ 2 |/σ 2 c 0 = 2.35 according to [16] does not exceed 0.16 even when ν = ∞.…”

“…Motivated by the fact that (9) takes its largest values when |µ 1 − µ 2 |/σ 2 c 0 , Wang and Iyer [16] suggested to test the validity of the claim, |µ 1 − µ 2 |/σ 2 c 0 , which is a non-conformance hypothesis. Designating non-conformity as a null hypothesis is commonly suggested when testing bioequivalence where a generic drug (which has to establish itself) must be compared with the brand name drug.…”

“…With X 1 denoting the measurand of lab 1, Willink [18] suggested to use E(X − X 1 ) 2 as a symmetric measure of compatibility of labs 1 and 2. Wang and Iyer [16] addressed the same issue and proposed a directional (asymmetric) interchangeability characteristic A 12 of two labs as Willink's coefficient normalized by 2σ 2 1 . When these variables have normal distributions,…”

Bias detection and certified reference materials for random measurands

“…A similar problem arises in interlaboratory comparisons when one of the labs is far more qualified than others in terms of trueness and precision (say, is considered to be a gold standard) [1,20]. In this case the coverage interval of the superior lab may be used to specify the parameters of the prior distribution.…”