GeneralizedLinearModelFit and offsert for poisson regression

• To: mathgroup at smc.vnet.net
• Subject: [mg112975] GeneralizedLinearModelFit and offsert for poisson regression
• From: Ester Vilaprinyó <evilaprinyo at cmb.udl.cat>
• Date: Sat, 9 Oct 2010 06:33:13 -0400 (EDT)

```Hello, I would like to solve a poisson regression with the
GeneralizedLinearModelFit function.
I have a matrix with the following form:

{{x11,x12, x13, y1},
{x21,x22, x23, y2},
...
}

The GeneralizedLinearModelFit for an exponential family Poisson will return
e^(b0+b1 f1+ b2 f2+ b3 f3)
Can I fix that b3=1?

In my case y refers to death counts and x3 to population. In other
programs such as Stata this would be solved by offset(x3). I tried to
solve this using LinearOffsetFunction but I did not succeed with the
following steps: 1) created a new matrix for data = {{x11,x12,
y1},{x21,x22, y2},...}. 2) Create a function that will return the offset
for each input f[x1_,x2_]:=x3 3)
GeneralizedLinearModelFit[data,{x1,x2},{x1,x2},ExponentialFaily->"Poisson",
LinearOffsetFunction->(f[#1,#2]&)]. Why it does not work?

Thanks!

```

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