[R] Insurance data in library(MASS)

[Prof Brian Ripley]

You are asking about support software for a book, and the book 
contains the answers ....  And it should be given due credit.

On Mon, 23 Feb 2009, choonhong ang 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 ?

See the book ca p.146.

> (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 ?

Who knows?: you did not deign to tell us what you did with the CSV 
file nor the results you got.  Most likely you did not get the factor 
levels and classes the same as the help file destribes.  Hint: Group 
and Age are ordered factors.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595