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st: Interval censoring using intcens


From   Patrick Munywoki <pmunywoki@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Interval censoring using intcens
Date   Sat, 28 Jul 2012 09:29:15 +0100

Hi,
I have been attempting to analyse interval censored time-to-event data
with 'intcens' ado (Griffin et al 2006). My data arise from a
longitudinal household-based study with nasal swab collections
twice-a-week for a duration of 26 weeks regardless of their any
symptoms. I want to be able to estimate the duration of infectious
period for one of the viruses we detected. I have reduced the data  to
one observation per infection episode in order to use the 'intcens'
command with t0 being the date last positive sample while t1 is the
date of the next negative sample. I hope this data conversion to
single observation per infection episode data is alright?

My questions?
1. How do i interpret the coefficient given in the results below?

intcens t0 t1 male, dist(exp) time nolog

stata output
Exponential distribution -      log acceleration factors

Uncensored               0
Right-censored           0
Left-censored            0
Interval-censored      188

        Number of obs   =       188
        Wald chi2(1)    =       0.00
Log likelihood =  -1796.982     Prob > chi2     =       0.9990


Coef.   Std. Err.      z    P>z     [95% Conf.  Interval]

male   -.0001871        .1470683    -0.00   0.999    -.2884356  .2880615
_cons    9.817517       .2234524    43.94   0.000     9.379558  10.25548

Note the actual interval between the dates t0 and t1 is on average(sd)
3.6 (0.98) days; median(IQR) 4 (3-4) days; and range 2-7 days.


2. Whenever i try using any other distribution this error message pops
up. What could be the problem here?
intcens t0 t1 male, dist(weib) time nolog
initial values not feasible
r(1400);

3. Is there an alternative method to the interval censoring which
allows me to use the multiple records per person accounting for the
interval censoring. I have tried stpm but not sure whether it allows
for this.

I would greatly appreciate your help ,

Many thanks,

--
Patrick Munywoki
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