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Re: st: using pscore and pstest


From   Steven Samuels <sjhsamuels@earthlink.net>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: using pscore and pstest
Date   Fri, 25 Apr 2008 07:57:07 -0400

-
Henrique, how were the program and beneficiary sub-samples selected? Are the beneficiary and control sampling units projects or households? Was there control of the number of the beneficiary and control units--for example to achieve approximately equal numbers, or minimum numbers of each?

-Steven
On Apr 24, 2008, at 8:32 PM, Henrique Neder wrote:


Dear
I have a problem with the use of the pscore and pstest commands. My sample
is a cluster sample in that the sample observations are selected by the
followings steps:

1 - The survey is made in five States and in each State we selected some
number of projects (the primary sample units - PSUs) in all sub- regions of
this State.

2 - In each project we selected a fixed number of households.

The sample weights are of the fweights form, calculated as the ratio -
number of households in each sub-region (universe) / the number of
households (observations) selected in the sample and inside that same
sub-region. Alternatively, we have a pweight, because the projects were
selected with PPS (with probability proportionate to the number of the
households in each project in the universe). This sample of projects were
selected as a sub-sample of the projects in a previous survey (that is, the
second survey was a subsample of the projects in the first survey).
We have in the survey two subsamples: a sub-sample of a program
beneficiaries and a control sub-sample.

I executed the commands pstest and pscore using a logit model with y = dummy
of participation program and yi (covariates) = variables that explain the
participation. In the first execution I executed the commands with
propensities scores obtained through non weighted logit regressions and some
models are balanced in the pstest and pscore commands. But when I use the
weighted logits, the balancing tests are not satisfied (the pscore command
stops and in the pstest the covariates are unbalanced with small p- values
and the conjoint chi-square test with low p-value, too).

My questions are:

1 - It is necessary to execute the commands with propensities scores
obtained through weighed logit regressions to estimate the atts?

2 - It is adequate to test balancing with pstest and pscore without weights
and estimate the atts with propensities scores obtained through weighted
logit regressions?

3 - I read that a sample proposal is to weight the treated observations with
the weight = 1 / propensity and the untreated with the weight = 1/(1 -
propensity). In my case, is this solution appropriate? Does it correct the
estimates considering the representation of the program effects in the
universe?

Best regards

Henrique Dantas Neder
Universidade Federal de Uberlāndia - Minas Gerais - Brazil

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