Hi,
I'm using matchit, in particular genetic matching. Although the matching
shows good balance on most pre-treatment covariates, there is one covariate
(a test score) that is not balanced well on (expectedly), because there is a
test score cutoff value which separates treatment and control groups. I have
already run a discontinuity analysis, but what I really want to do is match
the data on all pre-treatment covariates besides the score and then model a
linear relationship between the score and my outcome of interest. I was
wondering if I used zelig to interpolate/extrapolate a line after genetic
matching, would that serve my purposes? ALSO, If I use linear regression in
Zelig, how do I just for the covariate weights from genetic matching (if at
all), especially if I did matching of each treatment observations with 3
control observations (and with repeated draws)?
Any help would be greatly appreciated!
Thanks!
It's the latter. You can think of matching in observational studies as a
way to have the treatment and control groups that have similar covariate
distributions. From this perspective, it does not matter which units are
matched with each other. What matters is the resulting treatment and
control goups that have good covariate balance. Of course, if you do
subclassification, then the model will be estimated within each subclass.
Kosuke
--
Department of Politics
Princeton University
http://imai.princeton.edu
On Sat, 13 Jun 2009, Prashant wrote:
> Hi,
> I'm new to Zelig. I was trying to figure out how Zelig simulates the
> counterfactuals for a treatment group (after already having run matchit to
> get treatment and control groups) to estimate the ATT. I think in basic
> terms it estimates the parameters of a model (that you specify) for the
> matched control group and then uses the estimated parameters and treatment
> group's covariates to estimate predicted/expected values--these are the
> counterfactuals for the treatment group.
>
> But here's my question (and it is probably due to a lack of conceptual
> understanding): Sometimes matching is in pairs (for example)--does the
> simulation also take account for this? That is, if persons A, B, C in the
> treatment group are matched to persons D, E, F respectively in the control
> group, does the simulation take into account that matching has grouped A &
> D, B & E, C & F? Or does the simulation just take the mass of the matched
> control group observations and estimate a model through it to create
> estimated parameters (to be used with the treatment group's covariates to
> create counterfactuals)?
>
> Sorry in advance if the question is not clear.
>
> best,
> Prashant
>
--
MatchIt mailing list served by Harvard-MIT Data Center
List Address: matchit(a)lists.gking.harvard.edu
Subscribe/Unsubscribe: http://lists.gking.harvard.edu/?info=matchit
MatchIt Software and Documentation: http://gking.harvard.edu/matchit/
Browse/Search List Archive: http://lists.hmdc.harvard.edu/lists/matchit/
