The PSMATCH Procedure

STRATA Statement

STRATA <options>;

The STRATA statement divides observations in the support region into strata based on propensity scores, where the support region is specified in the REGION= option in the PROC PSMATCH statement.

The STRATA statement does not apply when you specify the MATCH statement. You can specify the following options:

NSTRATA=n

specifies the number of strata, where n 2. Only observations in the support region are stratified. By default, NSTRATA=5.

KEY=NONE | TREATED

specifies the type of observations that are used to construct the strata:

NONE: requests that each stratum contain approximately the same number of observations, which can be in either the treatment group or the control group.
TREATED: requests that each stratum contain approximately the same number of observations in the treatment group.

By default, KEY=TREATED.

For more information, see the section Propensity Score Stratification.