VARIATION OF FRACTIONATOR ESTIMATES AND ITS PREDICTION

Over the last decade the so-called 'fractionator' has become widesprea d in anatomical and pathological research for obtaining unbiased estim ates of total numbers of particles in biological specimens. Several me thods have been proposed for predicting the precision (i.e., the varia tion) of the estimated total numbers of particles using the fractionat or (i.e., for predicting the precision of fractionator estimates). How ever, the validity of these predicting methods has not been tested so far. As it is impossible to do so with biological experiments, it was carried out here by using a computer simulation. Specimens containing particles, with various particle distributional patterns, were modeled , and the total number of particles in the specimens was estimated rep eatedly with various modeled sampling schemes. It could be shown that the empirically estimated precision of the modeled fractionator estima tes depend on both the particle distributional pattern in a modeled sp ecimen as well as on the applied sampling scheme. Furthermore, conside rable differences between the predicted and the empirically estimated precision of the modeled fractionator estimates were found. This was d ue partly to an incorrect assumption, which serves as the basis for on e of the proposed predicting methods, partly to the fact that for some of the proposed predicting methods important contributions to the var iation of fractionator estimates have not been considered, and partly to the fact that the mathematical theory, which serves as the basis fo r all predicting methods proposed so far, can in principle not be the optimum basis for predicting the precision of fractionator estimates B ased on the results of the computer simulation, a new, simple method i s proposed for predicting the precision of fractionator estimates.