The influences of the between- and within-run components of variation on the mean rule

Most assays performed in chemistry and endocrinology laboratories have values ofsb which are non-zero with the ratio Sb/S, varying from 0.3 to 3 [2 and 3]. Westgard, Falk and Groth have recently used computer simulations to show how Sb and sw affected the performance characteristics ofvarious control rules [4 and 5]. Their simulations were based on a model that incorporated Sb, Sw and errors of varying sizes, either systematic or random. The simulations were used to obtain the probability of false rejection (Pfr), the probability of a rejection signal when no analytical error was present; and the probability of error detection (Peel), the probability of a rejection signal when an analytical error was present. They found that with significant Sb, there was deterioration in the performance characteristics of rules sensitive to systematic error, i.e. there was a tendency for Pfr tO increase and Pe, to decrease. They concluded that the optimal detection of systematic errors was difficult in the presence of significant Sb.