Re: st: Propensity Score Matching Between 3 Groups

[Fernando Rios Avila <f.rios.a@gmail.com>]

Hi Isobel,
So here is what I know about this.
If what you want to do is to indeed apply the propensity scores from
the A vs B group for the A vs C group, I would run the logit between A
and B, and then predict the propensity score for all three groups.
Once the propensity score is estimated, you can indicate within the
-psmatch2- the specific propensity score you want to use, instead of
having it estimate a separately logit model.
The other alternative, given that there is nothing that would indicate
that people in group B are equal to people in group C, is to estimate
the propensity score using a multinomial logit for the three groups,
and then proceed with your analysis with each pair group of interest.
(for example C vs B with B as treated group) (C vs A) and (B vs A)
Hope this helps.
Fernando


On Wed, Feb 26, 2014 at 2:01 PM, Isobel Williams
<iwilliams24@hotmail.com> wrote:
> Hi,
>
> I am trying to estimate a propensity score and then find the
> average treatment effect on the treated. However, my sample has 3
> groups:
>
> Group A: Resides in intervention area, receives treatment
> Group B: Resides in intervention area, doesn't receive treatment
> Group C: Resides in non-intervention area, doesn't receive treatment
>
> Thisis effectively like having 1 intervention group and 2 control groups: I
>  want to calculate a propensity score for treatment between Groups A and
>  B. I then want to apply this propensity score to Groups A and C to find
>  the average treatment effect on the treated.
>
> I have seen this done in several economic papers, but never explained thoroughly. Is it
> possible to do this in Stata, and if so, how?
>
> If it is relevant, I am using a logit model and -psmatch2- (the user-written SSC programme) to estimate the propensity score.
>
> Thanks!
> Isobel Williams
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