Estimation of the coefficient of variation from laboratory analysis of split specimens for quality control in...

An explicit statistical model is proposed for the coefficient of variation for laboratory analyses of constituents of blood, serum, saliva, or other specimens. A method for computing the maximum likelihood estimate of the key parameter is described, and compared with two simpler noniterative estimates. Validity of the model is explored by analysis of data from the central laboratory of a large cooperative clinical trial. Simulation studies are employed to compare the accuracy of the three estimators of the coefficient of variation. For most laboratory measurements for which the model is valid, one of the two noniterative estimates is nearly as accurate and unbiased as the maximum likelihood estimate.