The distribution of thetandzvariables in the case of stratified sample with individuals taken from normal parent populations with varying means
Martin Weibull · Scandinavian Actuarial Journal · 1950
If all N individuals x i in a certain sample are taken. out of one and the same normal parent population with the mean µ and the standard deviation it holds true that the sample's mean and variance in accordance with ,Student.-Fisher's theorem obey the frequency function