[R] poisson and peritonitis

[Troels Ring]

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

Troels

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