The PSMATCH Procedure

PROC PSMATCH Statement

The PROC PSMATCH statement invokes the PSMATCH procedure. Table 95.1 summarizes the options available in the PROC PSMATCH statement.

Table 95.1: Summary of PROC PSMATCH Options

Option	Description
DATA=	Specifies the input data set
REGION=	Specifies the support region of observations for stratification and matching

DATA=SAS-data-set

names the input SAS data set. If the propensity scores are to be derived from this data set, you must also include a PSMODEL statement to specify the binary logistic model. Otherwise, a PSDATA statement is required to identify the variable that contains either the propensity scores or the logits of propensity scores.

REGION=region <(region-options )>

specifies an interval region of propensity scores (or equivalently, logits of propensity scores) such that only observations that have propensity scores in the region are used in stratification and matching. This option also specifies the observations to be included in the output data set if the OUT(OBS=REGION) option is specified in the OUTPUT statement (even when the STRATA and MATCH statements are not specified). By default, REGION=TREATED if the MATCH statement is specified, and REGION=ALLOBS if the MATCH statement is not specified.

You can specify the following regions along with their region-options:

REGION=ALLOBS <( region-options )>

selects all available observations. You can specify the following region-options to select observations whose propensity scores lie in a specified range:

PSMIN=pmin: specifies the minimum propensity score in the support region, where pmin 0. Observations that have propensity scores that are less than pmin are excluded from the support region. By default, PSMIN=0, so that observations with small propensity scores are not excluded.
PSMAX=pmax: specifies the maximum propensity score in the support region, where pmax 1. Observations that have propensity scores that are greater than pmax are excluded from the support region. By default, PSMAX=1, so that observations with large propensity scores are not excluded.

You can also use the PSMIN= and PSMAX= options to exclude observations with extreme propensity scores from the output data set.

REGION=CS <( region-option )> REGION=TREATED <( region-option )>

selects the region of common support for the propensity scores for observations in the treated and control groups or the region of propensity scores for observations in the treated group only:

CS: selects observations whose propensity scores lie in the region of common support for the propensity scores for observations in the treated and control groups. This region is the widest interval such that both the treated and the control groups have subjects whose propensity scores lie within this interval. The lower endpoint of the region is the larger of the minimum propensity score for the treated group and the minimum propensity score for the control group. The upper endpoint is the smaller of the maximum propensity score for the treated group and the maximum propensity score for the control group.
TREATED: selects observations whose propensity scores lie in the region of propensity scores for observations in the treated group.

You can use the following region-option to extend the specified support region:

EXTEND <(ext-options )> = p <(LOWER=p UPPER=p )>

specifies extension to the lower and upper ends of the common support region (REGION=CS) or the range of treated observations (REGION=TREATED) for the support region, p 0. By default, EXTEND=0.25.

You can use the following ext-options to prescribe the extension requirement:

MULT=ONE | STDDEV

specifies the multiplier for the extension p to extend the support region:

ONE: extends the region by p.
STDDEV: extends the region by p the pooled estimate of the common standard deviation of the specified statistic, where this estimate is computed as the square root of the average of the variance of the PS (LPS) in the treated group and the variance of the PS (LPS) in the control group.

By default, MULT=STDDEV.

STAT=LPS | PS

specifies the type of the statistic that is used to extend the support region:

LPS: extends the region by using the logit of the propensity score.
PS: extends the region by using the propensity score.

By default, STAT=LPS.

The MULT= and STAT= ext-options prescribe the extension requirement as follows:

EXTEND(STAT=PS MULT=ONE)=p extends the specified support region by p in propensity score. That is, if denotes the propensity score interval region that is computed from the specified region, then the range of the extended support region is given by .
EXTEND(STAT=PS MULT=STDDEV)=p extends the specified support region by p , the square root of the average variance of the propensity score in the treated and control groups. That is, if denotes the propensity score interval region that is computed from the specified region, then the range of the extended support region is given by .
EXTEND(STAT=LPS MULT=ONE)=p extends the specified support region by p in the logit of propensity score.
EXTEND(STAT=LPS MULT=STDDEV)=p extends the specified support region by p , the square root of the average variance of the logit of propensity score in the treated and control groups.

You can specify one of the following two options to use an extension other than p:

LOWER=p: extends the lower end of the specified region by p, where p 0.
UPPER=p: extends the upper end of the specified region by p, where p 0.