The Inadequacy of Normal Distribution Models for the Establishment of Assigned Values in Control Sera. The Establishment of Assigned Values in Control Sera, II.

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Abstract
Four statistical models for the establishment of assigned values in a control serum which are based on the assumption of a normal distribution are compared. The 1st model results in .hivin.x .+-. 2s [.hivin.x = mean, s = estimation of the variance of the errors], whereas each of the following 3 models are based on a special analysis of variance. The distributional properties of the data [creatinine, glucose, urea, alanine aminotransferase (EC 2.6.1.2), aspartate aminotransferase (EC 2.6.1.1), creatine kinase (EC 2.7.3.2), .gamma.-glutamyltransferase (EC 2.3.2.2.)] of the study described in part 1 of this series were studied by means of appropriate statistical tests. Many model assumptions are violated: the totality of data of each method was never normally distributed, normal distribution within laboratories was not given in 27 of 67 cases, and precision and accuracy varied from reference laboratory to reference laboratory. Moreover, assigned values and uncertainty intervals calculated by means of these methods can be misleading to the customer. Therefore, these models cannot be applied and a distribution-free procedure has to be used instead.