st: RES: examples propensity score matching

 From "Henrique Neder" To Subject st: RES: examples propensity score matching Date Tue, 28 Oct 2008 17:00:35 -0200

```Ana Gabriela

Your data have to look like this:

Year group Varresult1 varresult2 covariate1 covariate2 ....
covariatek
Obs 1   t1  treat   ....       ....      ....
Obs 2   t1  contr
Obs 3

.....   t2  treat
Obs n   t1  contr

Where varresult is result variable and covariate are the covariates used in
logit/probit model.

If you have no counterfactual information for the period 1 refering about
result variables, you can´t estimate double difference but you estimate only
a cross section estimate for the period t2. Your covariates in the logit
model have to be dated in t1 (or more precisely prior to treatment). So, if
your treatment is dated in t1 or before and if you don?t observe the control
individuals in t1, it is impossible to estimate the propensity score. You
have to observe the covariates (used in the logit/probit model) prior the
treatment date unless all your covariates are fixed in time.

Henrique Neder

-----Mensagem original-----
De: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] Em nome de Ana Gabriela
Guerrero Serdan
Enviada em: terça-feira, 28 de outubro de 2008 16:08
Para: statalist@hsphsun2.harvard.edu
Assunto: st: examples propensity score matching

Dear Stata users,

A very basic question. I want to take a look at how to do a propensity score
matching in stata (commands psmatch2, pscore, I think).

I have two cross sectional surveys (t1, t2)  where I observe treatment and
control individuals in the second period but I cant know the conterfactual
in t1. I want to use propensity score matching to indivudals in t2 to
individuals in t1 based on some observable characteristics.

I have technical readings and literature but I would like to know the how to
in Stata. how the data should look? should I pool individuals for both
cross-sections?

thanks,
Gaby

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