Stratified sample

A sample which is broken up into several samples of smaller sizes by certain distinguishing marks (characteristics). Let each element of some sample of size possess one and only one of possible marks. Then the original sample can be broken into samples of sizes , respectively :

where the -th sample contains only those elements of the original sample which have the mark . As a result of this decomposition, the original sample becomes stratified into strata , , where the -th stratum contains information about the -th mark. This notion gives rise, for example, to realizations of the -component of a two-dimensional random variable whose second component has a discrete distribution.

References

[1]	S.S. Wilks, "Mathematical statistics" , Wiley (1962)

References

[a1]	W.G. Cochran, "Sampling techniques" , Wiley (1977)