[R] Survival analysis MLE gives NA or enormous standard errors

[Christopher David Desjardins]

Hi,
I am trying to fit the following model:   
     
sr.reg.s4.nore <- survreg(Surv(age_sym4,sym4), as.factor(lifedxm),
data=bip.surv)

Where age_sym4 is the age that a subject develops clinical thought
problems; sym4 is whether they develop clinical thoughts problems (0 or
1); and lifedxm is mother's diagnosis: BIPOLAR, MAJOR DEPRESSION, or
CONTROL.

I am interested in whether or not survival differs by this covariate.

When I run my model, I am getting the following output:

> summary(sr.reg.s4.nore)

Call:
survreg(formula = Surv(age_sym4, sym4) ~ as.factor(lifedxm), 
    data = bip.surv)
                           Value Std. Error     z       p
(Intercept)                4.037      0.455  8.86643
0.000000000000000000755
as.factor(lifedxm)CONTROL 14.844   4707.383  0.00315
0.997484052845082791450
as.factor(lifedxm)MAJOR    0.706      0.447  1.58037
0.114022774867277756905
Log(scale)                -0.290      0.267 -1.08493
0.277952437474223823521

Scale= 0.748 

Weibull distribution
Loglik(model)= -76.3   Loglik(intercept only)= -82.6
	Chisq= 12.73 on 2 degrees of freedom, p= 0.0017 
Number of Newton-Raphson Iterations: 21 
n=186 (6 observations deleted due to missingness)


I am concerned about the p-value of 0.997 and the SE of 4707. I am
curious if it has to do with the fact that the CONTROL group doesn't
have a mixed response, meaning that all my subjects do not develop
clinical levels of thought problems and subsequently 'survive'.

> table(bip.surv$sym4,bip.surv$lifedxm)
   
    BIPOLAR CONTROL MAJOR
  0      41      60    78
  1       7       0     6

Is there some sort of way that I can overcome this? Is my model
misspecified? Is this better suited to be run as a Bayesian model using
priors to overcome the lack of a mixed response?

Also, please cc me on an email as I am a digest subscriber.
Thanks,
Chris


-- 
Christopher David Desjardins
PhD student, Quantitative Methods in Education
MS student, Statistics
University of Minnesota
192 Education Sciences Building
http://cddesjardins.wordpress.com