WR

Literally, denotes "with replacement" sampling at the first stage. This is the default sample design for all SUDAAN procedures and leads to a variance computation procedure useful in many sample surveys and most experimental designs involving Cluster-correlated data in clinical, epidemiological, toxicological, and behavioral research. For all SUDAAN procedures, you can specify the sample design on the PROC statement, using the DESIGN option.

The default NEST statement specification for the WR design is:

NEST STRATA PSU;

where STRATA defines the stratification variable, and PSU defines the primary cluster variable. To define the entire population as a single stratum, use the SUDAAN keyword _ONE_ in place of STRATA.