st: stcrreg postestimation

[savagec@mskcc.org]

Hi all, 

I'm using STATA's new competing risk regression command, stcrreg.  I'm trying to use the postestimation commands, but am running into problems.  My aim is to calculate the 10-year predicted cumulative incidence of cause-specific death (non-cause specific death is the competing risk) by age and adjusted to the mean of another covariate in the model. 

To accomplish this, I ran the competing risks regression model:
. stset ttdeath, f(outcome==1)
. stcrreg age covariate1, compete(outcome==2)

Then I set covariate to the mean and asked STATA for the linear predictor (predict xb, xb). So far so good. 

The problem came when I tried to calculate the baseline cumulative incidence or cumulative subhazard.  The issues I noticed were:

- Baseline cumulative incidence and subhazard predictions changed depending on whether I predicted them before or after setting the covariates to the mean.  My understanding of these functions was that they are calculated for subjects who have zero-valued covariates - so why would manually changing the covariate have any impact?  Moreover, if I manually set the covariate to zero, I actually get the same predictions as when I had set it to the mean (which was different than when I did nothing to the covariate).  

Example:
. * predict baseline cumulative incidence BEFORE adjusting for covariate1
. predict basecif_before, basecif
. 
. * set covariate1 to the mean
. qui sum covariate1
. qui replace covariate1 = r(mean)
. 
. * predict baseline cumulative incidence AFTER adjusting for covariate1
. predict basecif_after, basecif
. 
. * predict baseline cumulative incidence after setting covariate to zero
. replace covariate1 = 0
(695 real changes made)

. predict basecif_zero, basecif

. sort _t

. list basecif_before basecif_after basecif_zero _t, ab(33)

     +-----------------------------------------------------------+
     | basecif_before   basecif_after   basecif_zero          _t |
     |-----------------------------------------------------------|
  1. |              0               0              0   .05475702 |
  2. |              0               0              0   .06023272 |
  3. |              0               0              0    .8295688 |
  4. |              0               0              0    .9336071 |
  5. |              0               0              0   1.1909651 |
     |-----------------------------------------------------------|
  6. |              0               0              0   1.3278576 |
  7. |       .0075787        .0121167       .0121167   1.3607118 |
  8. |       .0075787        .0121167       .0121167   1.5058179 |
  9. |       .0075787        .0121167       .0121167   1.5441478 |
 10. |       .0151121        .0241086       .0241086   1.7330595 |
     |-----------------------------------------------------------|
 11. |       .0151121        .0241086       .0241086   1.8918549 |
 12. |       .0151121        .0241086       .0241086   2.0999315 |
 13. |       .0225957        .0359711       .0359711   2.1629021 |
 14. |       .0225957        .0359711       .0359711   2.1793292 |

- Manually replacing _t to a particular time (say 10 years for calculating the cumulative incidence at 10 years) also causes incorrect predictions of the baseline cumulative incidence or subhazard.  When I predict without replacing _t, the prediction at 10 years is different than the prediction after replacing _t to 10.  

Continuing the list from above:
     +--------------------------------------------+
     | basecif_before   basecif_after          _t |
270. |       .4816974        .6463553   9.9219713 |
     |--------------------------------------------|
271. |       .4816974        .6463553   9.9383984 |
272. |       .4816974        .6463553   9.9383984 |
273. |       .4816974        .6463553   9.9603014 |
274. |       .4870247        .6520672   9.9958935 |
275. |       .4870247        .6520672   10.004107 |
     |--------------------------------------------|
276. |       .4923086        .6576962   10.031486 |
277. |       .4923086        .6576962   10.031486 |
278. |       .4975549         .663254   10.069816 |
279. |       .4975549         .663254   10.075291 |
280. |       .4975549         .663254   10.091718 |

. * and after replacing time (_t )to 10 years
. replace _t = 10
. predict basecif_10, basecif
. sum basecif_10

    Variable |       Obs        Mean    Std. Dev.       Min        Max
-------------+--------------------------------------------------------
  basecif_10 |       685    .7447103           0   .7447103   .7447103

- And lastly, none of the above combinations gives me values that match those from stcurve (which I am currently treating as the gold standard).

Any insight would be greatly appreciated.

Thanks,
Caroline





 
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