The number of cultures required to achieve a theoretical precision of 20% using various estimators vs m, the number of mutations per culture. Precision is the coefficient of variation, (σm /m) × 100%, where σ was calculated from Eq. 35 and 41 of reference (4) for the p0 method and the Lea-Coulson method of the median, respectively, and from Eq. 1 of reference (12) for the MSS-maximum-likelihood method. These equations were solved for C, the number of cultures, by setting σm /m = 0.2