Hi,

In the result shown, the District 1 is used as the base category.  How to
change to make District 4 as a base category ?

On Mon, Feb 23, 2009 at 11:05 AM, choonhong ang <angie.bearman@gmail.com>wrote:

> I have used the insurance data from R library and I have 2 questions:
> I use the following:
> >library(MASS)
> >data(Insurance)
> > m1=glm(Claims ~ District + Group + Age + offset(log(Holders)),data =
> Insurance, family = poisson)
> >summary(m1)
>
> Call:
> glm(formula = Claims ~ District + Group + Age + offset(log(Holders)),
>     family = poisson, data = Insurance)
> Deviance Residuals:
>      Min        1Q    Median        3Q       Max
> -2.46558  -0.50802  -0.03198   0.55555   1.94026
> Coefficients:
>              Estimate Std. Error z value Pr(>|z|)
> (Intercept) -1.810508   0.032972 -54.910  < 2e-16 ***
> District2    0.025868   0.043016   0.601 0.547597
> District3    0.038524   0.050512   0.763 0.445657
> District4    0.234205   0.061673   3.798 0.000146 ***
> Group.L      0.429708   0.049459   8.688  < 2e-16 ***
> Group.Q      0.004632   0.041988   0.110 0.912150
> Group.C     -0.029294   0.033069  -0.886 0.375696
> Age.L       -0.394432   0.049404  -7.984 1.42e-15 ***
> Age.Q       -0.000355   0.048918  -0.007 0.994210
> Age.C       -0.016737   0.048478  -0.345 0.729910
> ---
> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
> (Dispersion parameter for poisson family taken to be 1)
>     Null deviance: 236.26  on 63  degrees of freedom
> Residual deviance:  51.42  on 54  degrees of freedom
> AIC: 388.74
>  (1) In the result above, what is Group.L, Group.Q, Group.C, Age.L, Age.Q,
> Age.C ?
>
>  (2) When I copy the Insurance data in csv format (as shown in the
> attachement) and run the same procedure the result shown is different from
> above result, why ?
>

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