Sciensano , J. Wytsmanstraat 14 , 1050 Brussels , Belgium.
Department of Laboratory Diagnostics , General Hospital Pula , Zagrebačka 30 , 52100 Pula , Croatia.
Anal Chem. 2019 Feb 5;91(3):1847-1854. doi: 10.1021/acs.analchem.8b03313. Epub 2019 Jan 17.
Proficiency Testing (PT) External Quality Assessment (EQA) schemes are designed to ascertain the ability of individual laboratories to perform satisfactorily with respect to their peer laboratories or to limits imposed by external sources. Observed deviation of a laboratory result for a PT sample must be entirely attributed to the laboratory and not to the PT provider. To minimize the probability that deviations could be attributed to the PT provider, sample homogeneity should be assured. It is generally required that for quantitative parameters, the standard deviation among PT units should be calculated on the basis of duplicate measurements of at least 10 samples chosen at random, and the standard deviation among PT units should not exceed 0.3 times the standard deviation used to evaluate laboratories. Because this approach has important drawbacks, an alternative procedure is proposed by applying the theory of acceptance sampling to the assessment of sample heterogeneity for both quantitative and qualitative data and deriving acceptance limits on the basis of minimizing the probability of falsely evaluating laboratories. For obtaining acceptance limits for quantitative parameters, a distinction is made between laboratory evaluation using fixed limits on the one hand and laboratory evaluation using limits that are based on the variability of the reported results on the other hand. Sequential tests are proposed to evaluate sample heterogeneity by means of a comparison with the χ distribution. For qualitative parameters, acceptance-sampling plans are proposed that are based on minimizing the joint probability of rejecting batches that have a satisfactory amount of defective samples and accepting batches unnecessarily. The approach for quantitative parameters is applied on samples for a PT scheme of ethanol quantification and for qualitative parameters on the presence of monoblasts in a blood smear. It was found that five samples could already be enough to prove that the batch was homogeneous for quantitative parameters, although more than 20 samples were needed to prove homogeneity for qualitative parameters. This study describes a direct relation among the objective of an PT round, the criteria for evaluating the results, and the sample heterogeneity. When samples are effectively homogeneous, less measurements are needed than current practices require. A drawback of the proposed approach is that the number of samples to be tested is not known beforehand, and good knowledge of the analytical variability is crucial. The formulas to be applied are relatively simple. Despite the drawbacks, the proposed approach is generally applicable for both quantitative and qualitative data.
能力验证（PT）外部质量评估（EQA）方案旨在确定单个实验室相对于其同行实验室或外部来源规定的限制，是否具有令人满意的执行能力。实验室对 PT 样本结果的观测偏差必须完全归因于实验室，而不是 PT 提供者。为了最大程度地降低偏差归因于 PT 提供者的可能性，必须确保样本的均匀性。通常要求对于定量参数，PT 单位之间的标准差应基于至少 10 个随机选择的样本的重复测量来计算，并且 PT 单位之间的标准差不应超过用于评估实验室的标准差的 0.3 倍。由于这种方法存在重要的缺点，因此提出了一种替代程序，即将接受抽样理论应用于定量和定性数据的样本异质性评估，并根据最小化错误评估实验室的概率来推导接受限。对于定量参数，一方面区分了使用固定限对实验室进行评估，另一方面区分了使用基于报告结果变异性的限对实验室进行评估。提出了序贯检验来通过与 χ 分布的比较来评估样本异质性。对于定性参数，提出了基于最小化拒绝有满意数量缺陷样本的批次和不必要地接受批次的联合概率的接受抽样计划。该方法应用于定量参数的 PT 方案的乙醇定量样本和定性参数的血涂片单核细胞存在。结果发现，对于定量参数，即使需要 20 多个样本才能证明样本的均匀性，但是 5 个样本就足以证明批次的均匀性。本研究描述了 PT 轮的目标、结果评估标准和样本异质性之间的直接关系。当样本确实均匀时，所需的测量次数比当前实践要求的要少。所提出方法的一个缺点是，事先不知道要测试的样本数量，并且对分析变异性的良好了解至关重要。要应用的公式相对简单。尽管存在缺点，但所提出的方法通常适用于定量和定性数据。
