[R] poisson and peritonitis
Peter Dalgaard BSA
p.dalgaard at biostat.ku.dk
Tue Jan 23 00:14:42 CET 2001
Troels Ring <tring at mail1.stofanet.dk> writes:
> Dear friends. I have a very simple question. In an old paper (Vonesh,Stat
> Med 1990;9:263-271), the rate of peritonitis in 81 peritoneal dialysis
> patients is estimated. The estimated intercept and an effect for race (0,1)
> in a generalized linear model with poisson distribution is given. The
> patients are observed a different length of time but time is not in the
> model, so I cannot see how is accounted for that. Anyhow, the observed
> number of zero incidences (35) is compared to the fitted zero incidences
> (said to be 33.54).
> I would guess the way to do that was to let
> mm <- exp(0.00149+race*0.7888) (his intercept and effect for race)
> sum(dpois(0,mm)) but this doesn't yield but 25.64225
> I know the times, but how could I get to the results of Vonesh without
> letting it have an effect ?
> In hope of forgiveness if I have totally misunderstood what is going on
It can only be guesswork, but one idea could be that time actually
does enter but in the form exp(0.00149+race*0.7888)*time alias
exp(0.00149+race*0.7888+log(time)) which is a glim with an offset.
Then since the offset is known it might not be given in the results?
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907
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