Primary Sampling Unit (PSU)

In sample surveys, primary sampling unit (commonly abbreviated as PSU) arises in samples in which population elements are grouped into aggregates and the aggregates become units in sample selection. The aggregates are, due to their intended usage, called "sampling units." Primary sampling unit refers to sampling units that are selected in the first (primary) stage of a multi-stage sample ultimately aimed at selecting individual elements.

In selecting a sample, one may choose elements directly; in such a design, the elements are the only sampling units. One may also choose to group the elements into aggregates and choose the aggregates in a first stage of selection and then elements at a later stage of selection. The aggregates and the elements are both sampling units in such a ...