{smcl}
{* 9oct2002}{...}
{hline}
help for {hi:pscore}{right:(SJ2-4: st0026)}
{hline}


{title:Calculate the propensity score}


{p 12 19 2}
{cmd:pscore}
{it: treatment}
[{it:varlist}] 
[{it:weight}]
[{cmd:if} {it:exp}]
[{cmd:in} {it:range}]
{cmd:,}
{cmd:pscore}{cmd:(}{it:newvar}{cmd:)}
[{cmd:blockid}{cmd:(}{it:newvar}{cmd:)}
{cmdab:det:ail}
{cmd:logit}
{cmd:comsup}
{cmd:level}{cmd:(}{it:#}{cmd:)}
{cmd:numblo}{cmd:(}{it:#}{cmd:)}
]

{p 8 8 2}{cmd:fweight}s, {cmd:iweight}s, and {cmd:pweight}s are allowed;
see help {help weights}.


{title:Description}

{p 4 4 2} {cmd:pscore} estimates the propensity score (pscore) of the
{it:treatment} on {it:varlist} (the control variables) using a probit (or
logit) model and stratifies individuals in blocks according to the pscore;
displays summary statistics of the pscore and of the stratification; checks
that the balancing property is satisfied; if not satisfied asks for a less
parsimonious specification of the pscore; and saves the estimated pscore and,
optionally, the block number. The estimated propensity scores can then be
used together with {cmd:attr}, {cmd:attk}, {cmd:attnw}, {cmd:attnd}, and
{cmd:atts} to obtain estimates of the average treatment effect on the treated
using, respectively, radius matching, kernel matching, nearest neighbour
matching (in one of the two versions: equal weights and random draw), and
stratification, the latter using the block numbers as an input.


{title:Options}

{p 4 8 2} {cmd:pscore}{cmd:(}{it:newvar}{cmd:)} is required and asks users
to specify the variable name for the estimated propensity score,
which is added to the dataset.

{p 4 8 2} {cmd:blockid}{cmd:(}{it:newvar}{cmd:)} allows users
to specify the variable name for the block number of the estimated 
propensity score, which is added to the dataset.

{p 4 8 2} 
{cmd:detail} displays more detailed output documenting the steps performed to
obtain the final results.

{p 4 8 2} {cmd:logit} uses a logit model to estimate the
propensity score instead of the default probit model.

{p 4 8 2} {cmd:comsup} restricts the analysis of the balancing
property to all treated plus those controls in the region of
common support. A dummy variable named {it:comsup} is added to the
dataset to identify the observations in the common support.

{p 4 8 2} {cmd:level}{cmd:(}{it:#}{cmd:)} allows to set the
significance level of the tests of the balancing property. 
The default is 0.01.

{p 4 8 2} {cmd:numblo}{cmd:(}{it:#}{cmd:)} allows to set the
number of blocks of equal score range to be used at the beginning
of the test of the balancing hypothesis. The default is set to 5 blocks.
 

{title:Remarks} 

{p 4 4 2} Please remember to use the {cmd:update query} command before
running this program to make sure you have an up-to-date version of Stata
installed.  Otherwise, this program may not run properly.

{p 4 4 2} The treatment has to be binary.

{p 4 4 2} Make sure that the variables in varlist contain no missing values!

{p 4 4 2} With the option {cmd:detail}, 
the output of this program may be very long, but it offers useful
diagnostics to assess the validity of the propensity score approach
to the estimation of the ATT of interest. 


{title:Examples}

{p 4 8 2}{cmd:. pscore training age age2, pscore(mypscore)}

{p 4 8 2}{cmd:. pscore training age age2, pscore(mypscore) blockid(myblock) comsup}

{p 4 8 2}{cmd:. pscore training age age2, pscore(mypscore) logit level(0.001) numblo(10)}


{title:Authors}

	{browse "http://www.sobecker.de":Sascha O. Becker}
	Center for Economic Studies, University of Munich
 
	{browse "http://www.iue.it/Personal/Ichino":Andrea Ichino}
	Department of Economics, European University Institute, Florence
 
{p 4 4 2}Email {browse "mailto:so.b@gmx.net":so.b@gmx.net} or {browse "mailto:andrea.ichino@iue.it":andrea.ichino@iue.it} if you observe any problems.


{title:Also see}

{p 4 14 2} Online: help for {help atts}, {help attr}, {help attk}, 
{help attnw}, and {help attnd} (if installed). 

{p 14 14 2}Further details on the analytical formulas and on the algorithms 
used in these programs  can be found under  
{browse "http://www.sobecker.de":http://www.sobecker.de} 
or 
{browse "http://www.iue.it/Personal/Ichino":http://www.iue.it/Personal/Ichino}.
