Hi,
I'm using Stata 8.0 to test predictors of survival
(agecat, race, and gender) using Cox proportional
hazards regression. It gives me the following
output.
======================================================
. xi: stcox i.agecat i.race*i.gender
i.agecat _Iagecat_0-3 (naturally
coded; _Iagecat_0 omitted)
i.race _Irace_0-3 (naturally
coded; _Irace_0 omitted)
i.gender _Igender_0-1 (naturally
coded; _Igender_0 omitted)
i.race*i.gender _IracXgen_#_# (coded as above)
failure _d: cens24mo == 1
analysis time _t: ptime24mo
Iteration 0: log likelihood = -15962.398
Iteration 1: log likelihood = -15930.693
Iteration 2: log likelihood = -15930.117
Iteration 3: log likelihood = -15930.116
Refining estimates:
Iteration 0: log likelihood = -15930.116
Cox regression -- Breslow method for ties
No. of subjects = 13855
Number of obs = 13855
No. of failures = 1750
Time at risk = 4691755
LR
chi2(10) = 64.56
Log likelihood = -15930.116
Prob > chi2 = 0.0000
------------------------------------------------------------------------------
_t | Haz. Ratio Std. Err. z P>|z|
[95% Conf. Interval]
-------------+----------------------------------------------------------------
_Iagecat_1 | .9950285 .1272909 -0.04 0.969
.7743618 1.278578
_Iagecat_2 | 1.213802 .1492527 1.58 0.115
.9538532 1.544593
_Iagecat_3 | 1.631485 .2226493 3.59 0.000
1.248588 2.131802
_Irace_1 | 1.404169 .1757516 2.71 0.007
1.098701 1.794565
_Irace_2 | .8859186 .1215945 -0.88 0.377
.6769621 1.159373
_Irace_3 | .852908 .1614797 -0.84 0.401
.5884988 1.236115
_Igender_1 | .9002461 .0539135 -1.75 0.079
.8005434 1.012366
_IracXge~1_1 | 1.04967 .1669058 0.30 0.760
.768608 1.433509
_IracXge~2_1 | 1.075934 .1824927 0.43 0.666
.7716325 1.50024
_IracXge~3_1 | 1.046932 .2437096 0.20 0.844
.6633949 1.65221
------------------------------------------------------------------------------
. test _IracXgen_1_1 _IracXgen_2_1 _IracXgen_3_1
( 1) _IracXgen_1_1 = 0
( 2) _IracXgen_2_1 = 0
( 3) _IracXgen_3_1 = 0
chi2( 3) = 0.27
Prob > chi2 = 0.9660
=====================================================
Since the P >0.05 for the null hypothesis that the
interaction terms are equal to zero, is it safe to
conclude that there is no significant interaction
between race and gender?
Thanks,
Ashwin
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