My question is how to calculate the SE/95% CI for the predicted survival estimate from a parametric model in STATA. I know STATA is doing this with stcurve commands, but I haven't been able to figure out how to solve for a point estimate of survival and its SE for time t.
I have analyzed a large dataset of mule deer fawn survival (n~600) and Cox/parametric, and found a parametric (Weibull) model to be the best fitting parametric model (100's of dAIC units). One of the goals for our study is to understand the survival at some time t - i.e., for the winter of the study.
Given a Weibull equation, for a specific time, I then solve for the hazard at time t = 153 (our study period) to get a point estimate.
H(t) = exp(B0 + B1X...+ BnXn) tp for time t = 150 (length of the study)
For example, H(t) = 0.5795 for a female mule deer fawn of X mass, etc...
Thanks (in advance) for your help,
Mark Hebblewhite
The model results are pasted below:
Weibull regression -- log relative-hazard form
No. of subjects = 581 Number of obs = 2349
No. of failures = 253
Time at risk = 59812
LR chi2(9) = 139.61
Log likelihood = -477.86548 Prob > chi2 = 0.0000
------------------------------------------------------------------------------
_t | Coef. Std. Err. z P>|z| [95% Conf. Interval]
-------------+----------------------------------------------------------------
novdec | .0069395 .005974 1.16 0.245 -.0047693 .0186483
janmar | .0139184 .0044337 3.14 0.002 .0052284 .0226083
tminoct | .0416139 .0584366 0.71 0.476 -.0729197 .1561475
tminjm | -.1767656 .0550239 -3.21 0.001 -.2846105 -.0689206
tminnd | .0180625 .0631216 0.29 0.775 -.1056536 .1417786
october | -.0026746 .0051782 -0.52 0.606 -.0128237 .0074745
mass | -.1298777 .0215789 -6.02 0.000 -.1721716 -.0875838
male | .0924923 1.024433 0.09 0.928 -1.91536 2.100345
malemass | .0059718 .0296013 0.20 0.840 -.0520457 .0639894
_cons | -6.675164 .953159 -7.00 0.000 -8.543321 -4.807007
-------------+----------------------------------------------------------------
/ln_p | .4487272 .0714428 6.28 0.000 .3087019 .5887525
-------------+----------------------------------------------------------------
p | 1.566317 .1119021 1.361656 1.801739
1/p | .6384402 .045612 .5550192 .7343997
------------------------------------------------------------------------------
Sincerely,
Mark Hebblewhite
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Assistant Professor
Wildlife Biology Program
College of Forestry and Conservation
University of Montana
Missoula, MT, 59812
Office Phone: +1(406)-243-6675
Fax: +1(406)-243-4557
Email: [email protected]
http://www.cfc.umt.edu/HebLab/
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
