Dear Statalist,
I have categorized participants into 4 groups based on two baseline parameters to compare the mortality among groups. I tested the proportional hazard assumption using estat phtest, detail command, but the PH assumption is not met.
Here is what I got:
What would you suggest?
Thank you in advance.
I have categorized participants into 4 groups based on two baseline parameters to compare the mortality among groups. I tested the proportional hazard assumption using estat phtest, detail command, but the PH assumption is not met.
Here is what I got:
PHP Code:
stptime, per(1000) by(gr)
failure _d: event == 1
analysis time _t: t_eventyears
id: ID
Group | person-time failures rate [95% Conf. Interval]
-----------+-----------------------------------------------------------
GR_1 | 30375.285 150 4.9382252 [ 4.20795 5.795237]
GR_2 | 12924.76 99 7.6597168 [6.29019 9.327423]
GR_3 | 1523.6044 29 19.033812 [13.22701 27.38987]
GR_4| 2167.1376 7 3.2300672 [1.539883 6.775409]
-----------+-----------------------------------------------------------
total | 46990.787 285 6.0650186 [5.400218 6.81166]
. stcox i.gr, nolog
failure _d: event == 1
analysis time _t: t_eventyears
id: ID
Cox regression -- Breslow method for ties
No. of subjects = 10,111 Number of obs = 10,111
No. of failures = 285
Time at risk = 46990.78722
LR chi2(3) = 42.49
Log likelihood = -2509.9229 Prob > chi2 = 0.0000
-------------------------------------------------------------------------------------------------------
_t | Haz. Ratio Std. Err. Z P>|z| [95% Conf. Interval]
--------------------------------------+----------------------------------------------------------------
gr |
GR_2 | 1.553045 .2011129 3.40 0.001 [1.204917 2.001756]
GR_3 | 3.885477 .7882809 6.69 0.000 [2.61068 5.782759]
GR_4 | .6511265 .2517825 -1.11 0.267 [.3051521 1.389359]
-------------------------------------------------------------------------------------------------------
Test of proportional-hazards assumption
Time: Time
----------------------------------------------------------------
rho chi2 df Prob>chi2
------------+---------------------------------------------------
1b.gr . . 1 .
2.gr 0.09032 2.33 1 0.1272
3.gr 0.21086 12.71 1 0.0004
4. gr 0.22599 14.52 1 0.0001
------------+---------------------------------------------------
global test 25.16 3 0.0000
----------------------------------------------------------------
Thank you in advance.
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