RE: st: RE: gpscore for propensity score of 4 observed groups

[oconnor7@u.washington.edu]

Ok, thank you Juan!



On Tue, 12 Oct 2010, Villa Lora, Juan Miguel wrote:

> no, you misunderstood. A control group is what you need. But I would expect a 'clean' control group without any kind of treatment or a 'placebo taker'. If you want to use a control group with certain grade of treatment you won't get a reliable causal inference. I recommend an article found at http://ftp.iza.org/dp4451.pdf "Evaluating Nonexperimental Estimators for Multiple Treatments: Evidence from Experimental Data"
> ________________________________________
> From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] On Behalf Of oconnor7@u.washington.edu [oconnor7@u.washington.edu]
> Sent: Tuesday, October 12, 2010 6:09 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: RE: st: RE: gpscore for propensity score of 4 observed groups
>
> Thanks for your help. Yes, actually the groups consist of three levels of TBI severity and a control group of arm injured patients. Sorry for the confusion. I did not think that having a control would affect the propensity score in this situation.
>
> Stephen
>
> On Tue, 12 Oct 2010, Villa Lora, Juan Miguel wrote:
>
> > Stephen,
> > I haven't dealt with such case. Anyway, it seems to me that you don't have a control or comparison group without treatment. This situation may confound your evaluation and your results will be invalid.
> > Juan
> >
> > ________________________________________
> > From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] On Behalf Of oconnor7@u.washington.edu [oconnor7@u.washington.edu]
> > Sent: Tuesday, October 12, 2010 5:32 PM
> > To: statalist@hsphsun2.harvard.edu
> > Subject: Re: st: RE: gpscore for propensity score of 4 observed groups
> >
> > Hi Juan,
> >
> > Yes, this is true, the treatment variable is categorical. I was worried that this would be an issue. That said, what command what provide a propensity score for a categorical variable with four levels?
> >
> > Stephen
> >
> > On Tue, 12 Oct 2010, Villa Lora, Juan Miguel wrote:
> >
> > > Hey Stephen!
> > > Before answering your question I'd like to understand your treatment variable. You are stressing that you got four different groups, which makes me think that you are dealing with a categorical variable instead of a continuous variable as it's required for gpscore. Remember that Hirano and Imbens (2005) spell out that this treatment variable must be a normal distributed (one of the basic assumptions of the analysis).  Are you sure your treatment variable is continuous?
> > > Juan
> > > ________________________________________
> > > From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] On Behalf Of oconnor7@u.washington.edu [oconnor7@u.washington.edu]
> > > Sent: Tuesday, October 12, 2010 5:15 PM
> > > To: statalist@hsphsun2.harvard.edu
> > > Subject: st: gpscore for propensity score of 4 observed groups
> > >
> > > Hi,
> > >
> > > I have technical question regarding gpscore.
> > >
> > > If my treatment variable is type of injury severity, what should I put for "cutpoints", "index", and "nq_gps"? The treatment level has four different levels of injury severity.
> > >
> > > What I am seeking is to create a propensity score for the likelihood that a person develops a certain type of injury, in this case TBI, based upon a list of covariates.
> > >
> > > This is the syntax I used for a preliminary analysis:
> > >
> > > gpscore  age child_gender prev_anxiety prev_depn prev_adhd prev_behavioral prev_other_mh, t(inj_severity) gpscore(mygps) predict(hat_inj_sev) sigma(hat_sd) cutpoints (inj_severity) index(p50) nq_gps(4)
> > >
> > > Again, I am unsure of cutpoints, index, and nq_qps given that I have four established groups for the treatment variable.
> > >
> > >
> > > Thank you,
> > > Stephen
> > >
> > >
> > >
> > >
> > > Stephen O'Connor
> > > Senior Fellow
> > > Harborview Injury Prevention & Research Center
> > > Department of Psychiatry & Behavioral Sciences
> > > University of Washington at Harborview Medical Center
> > >
> > >
> > >
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