Segregated population, estimation

Estimation of Number and Size of Increments for a Segregated Population... 

When the target population is segregated, or stratified, equation 7.5 provides a poor estimate of the amount of sample needed to achieve a desired relative standard deviation for sampling. A more appropriate relationship, which can be applied to both segregated and nonsegregated samples, has been proposed. ... 

Statistics and probability theory provided the analyst with the theoretical framework that predicts the uncertainties in estimating proj rties of populations when only a part of the population is available for investigation. Unfortunately this theory is not well suited for analytical sampling. Mathematical samples have no mass, do not segregate or detoriate, are cheap and are derived from populations with nicely modelled composition, e.g. a Gaussian distribution of independent items. In practice the analyst does not know the type of distribution of the composition, he has usually to do with correlations within the object and the sample or the number of samples must be small, as a sample or sampling is expensive. 

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