Re: st: stcox after psmatch2

[Eduardo Nunez <enunezb@gmail.com>]

George,
You should look at ipw, an R package that estimate a propensity score
and use it as inverse probability weighting. The software allows
longitudinal data with survival endpoint.
Best wishes,
Eduardo


On Fri, May 11, 2012 at 5:35 AM, George Gunapal Pradeep Paul (NHGHQ)
<pradeep_paul_g_gunapal@nhg.com.sg> wrote:
>
> Thanks Ariel, Steve and Joerg for your suggestions and references. To
> clarify more,
>
> I am comparing a group of Chronic Obstructive Pulmonary Disease
> (COPD)patients enrolled in a disease management program and a control group
> selected from a administrative database. There is an enrolment criteria for
> enrolling patients into the program, but however not all COPD patients are
> enrolled.
>
> I sampled control cases from hospital administrative database, i.e. COPD
> patients who fulfilled the COPD disease management program's enrolment
> criteria but where not enrolled into the program. Now that I have program
> patients and controls, I did matching to adjust for the difference in
> characteristics on who gets enrolled into the program. For eg. If younger,
> more healthier patients are more often enrolled in the COPD disease
> management program, then we can expect them to have better outcomes (lower
> mortality) than the control group.
>
> My hypothesis: No difference is mortality rate (expressed in person years)
> between the patients enrolled in a COPD program and controls who were not
> enrolled in the program.
>
> Other things to consider, multiple records per patient and the follow time
> is different between the program patients and controls.
>
>
> Steve & Joerg: Since follow up period is different for these two groups,
> hence i thought of doing cox regression to adjust for the effect of follow
> up time on mortality on the matched program patients and controls. Kindly
> let me know your thoughts.
>
> Ariel:
> I used the following code for generating pscore and matching
>
> xi:pscore Status age i.gender_coded i.Race_coded i.Hospital_coded
> i.Patient_class_coded i.Asthma i.copd i.dm i.ht i.Stroke i.chd i.hf
> i.Dyslipidaemia i.Obesity if PrimaryFirst1==1, pscore(mypscore)
> blockid(myblock) comsup
>
> xi:psmatch2 Status if PrimaryFirst1==1, pscore(mypscore)
> outcome(i.Mortality_resp_system) caliper(.001) noreplace neighbor(1)
>
> And after matching, I identified pair count using the following code
> gen pair = _id if _treated==0
> replace pair = _n1 if _treated==1
> bysort pair: egen paircount = count(pair)
>
> I used one matched control per treated, I selected paircount=2 and did
> stcox regression. Am i doing it the right way?
>
>
> Thank you for your time and greatly appreciate your help.
>
> Best regards,
> Pradeep
>
>
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Ariel Linden,
> DrPH
> Sent: Thursday, May 10, 2012 11:52 PM
> To: statalist@hsphsun2.harvard.edu
> Subject: re: st: stcox after psmatch2
>
> I am not sure what problem your facing? -psmatch2 (a user written program
> found on ssc) will gives you a field called _nn that tells you who the
> matched control is. BTW, you didn't give details of which matching approach
> you used or how many controls. If you used more than one matched control per
> treated, you'll need the _weight variable as well.
>
> You then run your stcox model on only those patients and their matched
> controls (1:1), and if you have 1:k matches, you also include the _weight in
> the model...
>
> I hope this helps
>
> Ariel
>
> Date: Thu, 10 May 2012 05:33:22 +0000
> From: "George Gunapal Pradeep Paul (NHGHQ)"
> <pradeep_paul_g_gunapal@nhg.com.sg>
> Subject: st: stcox after psmatch2
>
> Dear all,
> I am comparing a group of Chronic Obstructive Pulmonary Disease
> (COPD)patients enrolled in a disease management program and a control group.
> I calculated pscore and did psmatch2 using c:\ado\plus\p\psmatch2.ado *!
> version 4.0.5 18apr2012 E. Leuven, B. Sianesi. I used psmatch2 to adjust
> for their baseline differences and now I would like to do a cox regression
> on the matched program patients and controls to see if there is a difference
> in time to death between the two groups.
>
> I would like to know how to run stcox after psmatch2 , thereby identifying
> the matching sequence for the cox regression. I tried looking for answers
> for this but found only one unanswered relevant question which could be
> found at http://www.stata.com/statalist/archive/2009-11/msg00709.html
>
> Kindly help.
>
> Thank you,
>
> Best regards,
> Pradeep
>
>
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