R help - Jun 2010 - glm poisson function

Hi,

I'm totally new to R so I apologise for the basic request. I am looking at
the incidence of a disease over two time periods 1990-1995 and 2003-2008. I
have counts for each year, subdivided into three disease categories and by
males/females.
I understand that I need to analyse the data using poisson regression and
have managed to use the pois.daly function to get age-sex adjusted rates and
corresponding confidence intervals. However, I now want to know how get a p
value (I'm writing up a paper for a journal) to say that x number of cases
in the first cohort (1990-1995) is significantly lower than y number in the
later cohort (2003-2008). I also want to make sure that I've corrected for
overdispersion etc.
I'm totally stuck and can't think where to start with writing a script.
So
basically my question is:
e.g. I have 271 cases of the disease between 1990-1995 (total population at
risk over six years = 6,164,113) and 433 cases between 2003-2008 (total
population at risk over sic year = 5,572,041) - is this significant and what
is the P value.
Any help much appreciated!
Cheers
P
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> prop.test(c(271,433),c(6164113,5572041))
         2-sample test for equality of proportions with continuity correction

data:  c(271, 433) out of c(6164113, 5572041)
X-squared = 54.999, df = 1, p-value = 1.206e-13
alternative hypothesis: two.sided
95 percent confidence interval:
  -4.291428e-05 -2.457623e-05
sample estimates:
       prop 1       prop 2
4.396415e-05 7.770941e-05



At 06:36 AM 6/10/2010, Phender79 wrote:
>Hi,
>
>I'm totally new to R so I apologise for the basic request. I am looking
at
>the incidence of a disease over two time periods 1990-1995 and 2003-2008. I
>have counts for each year, subdivided into three disease categories and by
>males/females.
>I understand that I need to analyse the data using poisson regression and
>have managed to use the pois.daly function to get age-sex adjusted rates and
>corresponding confidence intervals. However, I now want to know how get a p
>value (I'm writing up a paper for a journal) to say that x number of
cases
>in the first cohort (1990-1995) is significantly lower than y number in the
>later cohort (2003-2008). I also want to make sure that I've corrected
for
>overdispersion etc.
>I'm totally stuck and can't think where to start with writing a
script. So
>basically my question is:
>e.g. I have 271 cases of the disease between 1990-1995 (total population at
>risk over six years = 6,164,113) and 433 cases between 2003-2008 (total
>population at risk over sic year = 5,572,041) - is this significant and what
>is the P value.
>Any help much appreciated!
>Cheers
>P
>--
>View this message in context: 
>http://r.789695.n4.nabble.com/glm-poisson-function-tp2250210p2250210.html
>Sent from the R help mailing list archive at Nabble.com.
>
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>PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.
===============================================================Robert A.
LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral at lcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
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