Laboratory analytes for individuals are subject to several sources of variation, including biological variation, preanalytical variation (specimen collection), analytical variation (bias and imprecision), and postanalytical variation (reporting of results). Biological variation consists of within-person (WP) and between-person (BP) variation. These components of biological variation are used to set analytical quality specifications for bias and imprecision, evaluate serial changes in individual analytes, and assess the clinical utility of population-based reference intervals. Desirable quality specifications for imprecision (I), bias (B), and total error have been related to the WP CV ([CV.sub.w]) and the BP CV ([CV.sub.g]) of laboratory analytes (1-3). Imprecision should be ideally less than one half of the [CV.sub.w,] and bias should be 0.25[[([CV.sub.w])Z + ([CV.sub.g]).sup.2].sup.1/2.] The quality specification for total error is to be less than kI + B, where k = 1.65 at [alpha] = 0.05. The total CV ([CV.sub.t]) can be estimated assuming that the CVs of all sources are measured at the same analyte mean and that pre- and postanalytical sources of variation are negligible. The [CV.sub.t] = [([CV.sub.a]).sup.2] + [([CV.sub.w]).sup.2].sup.1/2], where the analytical CV ([CV.sub.a]) equals the laboratory method imprecision ([CV.sub.i]) if there is no bias present.
