Probabilities of selection are allotted according to size for which information is collected on an auxiliary variable or what is sometimes known as ancillary or supplementary variable.

To illustrate the method of this type of sampling, let us take an example. Suppose there are 10 households in a village with land holdings of varying sizes. We want to select 3 households for a farm experiment. We decide that in order to draw varying sizes. We want to select 3 households for a farm experiment. We decide that in order to draw a sample, the probabilities of selection will be proportional to the size of holding to each of the households.