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


From   [email protected]
To   "[email protected]" <[email protected]>
Subject   RE: st: RE: gpscore for propensity score of 4 observed groups
Date   Tue, 12 Oct 2010 15:24:12 -0700 (PDT)

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: [email protected] [[email protected]] On Behalf Of [email protected] [[email protected]]
Sent: Tuesday, October 12, 2010 6:09 PM
To: [email protected]
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: [email protected] [[email protected]] On Behalf Of [email protected] [[email protected]]
Sent: Tuesday, October 12, 2010 5:32 PM
To: [email protected]
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: [email protected] [[email protected]] On Behalf Of [email protected] [[email protected]]
Sent: Tuesday, October 12, 2010 5:15 PM
To: [email protected]
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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