[R] Poisson Regression
Martyn Plummer
plummer at iarc.fr
Fri Mar 28 12:57:05 CET 2003
On Fri, 2003-03-28 at 12:49, Meles MELES wrote:
> Hi,
> somebody asked me to do a Poisson regression on cancer incidence over
> years to see wether if there is a descending or an ascending tendancy.
> I tried with R, but it complains that the data are not integer but
> floating poing data. So, as I never did that sort of thing before, I'm a
> bit lost.
>
> the data serie looks like this
> SEX PERIOD INCIDENCE
> 1 [1978;1982] 57,3
> 1 [1983;1987] 58,3
> 1 [1988;1992] 65
> 1 [1993;1997] 56,8
> 2 [1978;1982] 4,6
> 2 [1983;1987] 5
> 2 [1988;1992] 5,1
> 2 [1993;1997] 6,2
>
> Any suggestions?
You don't have enough information. You need the number of events (y) and
the number of person-years at risk (pyar) separately. What you have is
the incidence rate (y/pyar) * (some scale factor).
With the correct data, your model will look something like this
glm(y ~ sex + period + offset(log(pyar)), family=poisson)
Judging by the PERIOD variable, I guess that you are looking at cancer
incidence data from volumes V to VIII of "Cancer Incidence in Five
Continents". In this case it is possible to reconstruce the original
age-specific incidence data from the published incidence rate and the
population pyramid data.
Martyn
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