Re: st: RE: graphing interactions after -stpm2-

[Adam Olszewski <adam.olszewski@gmail.com>]

Thank you very much! This works perfectly well!
Adam Olszewski

On Tue, Aug 27, 2013 at 12:07 PM, Lambert, Paul (Prof.)
<pl4@leicester.ac.uk> wrote:
> Adam,
>
> The syntax parsing does not appear to work properly for hrnum()/hrdenom() when there is an  interaction between a categorical and continuous covariate. I will fix this in the next update.
>
> In the meantime, you can either create your own interaction or use the -partpred- command available from SSC. See below,
>
> sysuse cancer.dta, clear
> recode drug 1=0 2/3=1
> // creating own interaction
> gen drug_age = drug*age
> stpm2 drug age drug_age, df(3) eform sca(h)
> predict hr1 if drug==1, hrnum(drug 1 drug_age .) hrdenom(drug 0) ci
> line hr1 hr1_lci hr1_uci age, sort name(g1, replace)
>
> // using partpred
> stpm2 drug##c.age, df(3) eform sca(h)
> partpred hr2 if drug == 1, for(1.drug 1.drug#c.age)  ci(hr2_lci hr2_uci) eform
> line hr1 hr1_lci hr1_uci age, sort name(g2, replace)
>
> Paul
>
>
> Professor Paul C Lambert
> Professor of Biostatistics
> Department of Health Sciences
> University of Leicester
> 2nd Floor, Adrian Building
> University Road
> Leicester LE1 7RH
> Tel: +44 (0)116 229 7265, Fax: +44 (0)116 229 7250
> e-mail: paul.lambert@le.ac.uk
> Homepage: http://www2.le.ac.uk/Members/pl4/
>
>
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Adam Olszewski
> Sent: 27 August 2013 05:07
> To: statalist@hsphsun2.harvard.edu
> Subject: st: graphing interactions after -stpm2-
>
> Hello,
> I was wondering if someone could advise me about how to graph an interaction effect between a categorical and continuous variable in a survival model. Specifically, I would like to fit a model with interaction and then plot the hazard ratio for the categorical variable on Y-axis against the continuous predictor on X-axis.
> I would like to do it fitting a flexible parametric model using the user-written -stpm2- command (available from SSC).
>
> I imagine the series of commands being something like:
>
> sysuse cancer.dta
> * binarize for simplicity
> recode drug 1=0 2/3=1
> stpm2 drug##c.age, df(3) eform sca(h)
> * predict hr, (..... - this is what I cannot figure out line hr age
>
> I tried various permutations of hrnum/hrdenom option as well as margins, but I cannot get the right result. I would imagine that predict hr, hrn(drug 1 age .) hrd(drug 0 age .) should work, but it produces a flat line. I assume I am missing something simple.
> A solution for a Cox model might help too, since perhaps I could figure out the stpm2 equivalent.
>
> Best,
> Adam Olszewski
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