Hello,
I have run the same Cox regression analysis with and without -parmby-, with
different results. The point estimate is the same, but the bootstrap
standard errors differ. Can anybody suggest why this would happen?
without -parmby-
. stcox tcm if stageII==1
No. of subjects = 65.6225431 Number of obs = 33
No. of failures = 65.6225431
Time at risk = 3532.264538
Wald
chi2(1) = 0.66
Log likelihood = -214.28476 Prob > chi2 = 0.4154
------------------------------------------------------------------------------
| Observed Bootstrap Normal-based
_t | Haz. Ratio Std. Err. z P>|z| [95% Conf. Interval]
-------------+----------------------------------------------------------------
tcm | .7248583 .2863995 -0.81 0.415 .3341442 1.572433
------------------------------------------------------------------------------
with -parmby-
. parmby "bootstrap, reps(1000): stcox tcm if stageII==1", ///
label command eform saving(tf_unst_II, replace) idnum(411)
idstr(Stage II) for(estimate min95 max95 %8.2f p %8.3f) ///
stars(0.05 0.01 0.001 0.0001) ///
list(idnum idstr parm label estimate min95 max95 p stars if
parmseq==1, clean noobs)
No. of subjects = 65.6225431 Number of obs = 33
No. of failures = 65.6225431
Time at risk = 3532.264538
Wald chi2(1) = 0.79
Log likelihood = -214.28476 Prob > chi2 = 0.3750
------------------------------------------------------------------------------
| Observed Bootstrap Normal-based
_t | Haz. Ratio Std. Err. z P>|z| [95% Conf. Interval]
-------------+----------------------------------------------------------------
tcm | .7248583 .2629041 -0.89 0.375 .3560612 1.475644
------------------------------------------------------------------------------
Best wishes,
Michael
____________________________________
Michael McCulloch
Pine Street Clinic
Pine Street Foundation
124 Pine Street, San Anselmo, CA 94960-2674
tel 415.407.1357
fax 415.485.1065
email: [email protected]
web: www.pinest.org
www.pinestreetfoundation.org
www.medepi.net/meta
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