Estimating viral concentrations from dilution counts: a reliable computation method programmed on a pocket calculator.

A program for a Hewlett-Packard 41C calculator is described, applying the maximum likelihood method for the estimation of the density of a suspension of infective particles when counts are available for a number of independent dilutions of the original suspension. An unbiased estimate for the variance of the density, a suitable confidence interval and its corresponding confidence level are also given by the program. Moreover, after testing for the presence of overcrowding and/or clumping, the selection of suitable dilutions is fully automated so as to avoid recourse to statistical tables.