[Relation between variance and the arithmetic mean in frequency distributions under conditions of stochastic...

While the average value of the mitotic index in a primordium is determined by genetic and epigenetic factors, the spatial location of the single mitotic events is stochastic; consequently mitotic density is uneven even in homogeneous areas of the primordium. The statistical frequency distribution of the mitotic events has been studied under three different conditions: (a) no stochastic dependence between adjoining events (random distribution); (b) positive stochastic dependence (facilitation) between adjoining events; (c) negative stochastic dependence (inhibition) between adjoining events. It is concluded that in the first case the variance of the distribution equals the arithmetic mean; in the second case the variance is higher than mean; in the third case variance is lower than mean.