Re: st: -svy stocx- attained age

[Steve Samuels <sjsamuels@gmail.com>]

Pradip:

You are encountering a version of problem that I diagnosed earlier this
month at http://www.stata.com/statalist/archive/2013-07/msg00644.html,
where I referred to
http://www.stata.com/support/faqs/statistics/stcox-producing-missing-standard-errors/
"4) Covariate does not vary within death event risk sets."

In your case, people in the same age group at baseline will have the
same attained age at all points of followup. You can use either age at
baseline or time as attained age, but not both.

I'd recommend age at baseline, as you know this pretty precisely, a gain
that doesn't transfer to attained age. But the use of only five age groups
loses a lot of information; try fractional polynomial regression (-fp-)
on continuous age.

In a post to me, you stated that you have a maximum of 10 years of
follow-up and, that for dates of death and interview, you have only year
and quarter. Your solution is to assign the midpoint date of each
quarter. This could work, but violates the assumption of -stcox- that
times are essentially continous. The measurement error in follow-up time
could be as much as ±3 months and will probably bias the estimated
coefficients. Moreover, if someone died in < 3 months after baseline,
you would be assigning start and death to the same date, and -stset-
will drop the observation.

Therefore I suggest that you also do a grouped hazard analysis with
-cloglog- which accepts a -svy- prefix. (-stpm2-, as you reminded me,
does not.). With -cloglog-, assign the person who died < 3 months after
baseline to the first period. For more details, see the the Lesson 6
link to discrete data analysis on Stephen Jenkins's fine web page
"Survival analysis with Stata"
(http://www.iser.essex.ac.uk/survival-analysis )

Steve



On Jul 31, 2013, at 12:53 PM, Muhuri, Pradip (SAMHSA/CBHSQ) wrote:

Hello,

I am new to the Statalist. In response to my first posted e-mail to the
List, and I got a reply from Steve, with insightful comments and advice.
At this point, I need your help with two issues.

1) All my subsequent e-mails (content --copied from the Stata log file -
in plain text, not html) have bounced back to me. I don't understand
what I am doing wrong.

2) I am using -svy:stcox- models, with attained age as the time scale. I
have successfully run several models. However, the addition of a
5-category factor (attained age) to the model gives me the following
error message: "flat region resulting in a missing likelihood error
occurred when svy executed stcox last estimates not found". Sorry I am
not pasting the content from the log file, fearing that this e-mail will
also bounce back.


Thanks,

Pradip

Pradip K. Muhuri, PhD SAMHSA/CBHSQ 1 Choke Cherry Road, Room 2-1071
Rockville, MD 20857 Tel: 240-276-1070 Fax: 240-276-1260


* * For searches and help try: * http://www.stata.com/help.cgi?search *
http://www.stata.com/support/faqs/resources/statalist-faq/ *
http://www.ats.ucla.edu/stat/stata/

On Jul 31, 2013, at 12:53 PM, Muhuri, Pradip (SAMHSA/CBHSQ) wrote:

Hello,

I am new to the Statalist. In response to my first posted e-mail to the List, and I got a reply from Steve, with insightful comments and advice.  At this point, I need your help with two issues.

1) All my subsequent e-mails (content --copied from the Stata log file - in plain text, not html) have bounced back to me. I don't understand what I am doing wrong. 

2) I am using -svy:stcox- models, with attained age as the time scale. I have successfully run several models. However, the addition of a 5-category factor (attained age) to the model gives me the following error message: "flat region resulting in a missing likelihood error occurred when svy executed stcox last estimates not found".  Sorry I am not pasting the content from the log file, fearing that this e-mail will also bounce back. 


Thanks,

Pradip

Pradip K. Muhuri, PhD
SAMHSA/CBHSQ
1 Choke Cherry Road, Room 2-1071
Rockville, MD 20857
Tel: 240-276-1070
Fax: 240-276-1260


*
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*   http://www.stata.com/support/faqs/resources/statalist-faq/
*   http://www.ats.ucla.edu/stat/stata/


*
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*   http://www.ats.ucla.edu/stat/stata/