# [R] R question - combine values

David Winsemius dwinsemius at comcast.net
Thu Feb 26 06:14:09 CET 2009

```You don't.

And even if you do get someone to tell you how, you may still not
legitimately lower your degrees of freedom. Friends don't let friends
use stepwise approaches to regression analysis.

--
David Winsemius

On Feb 25, 2009, at 10:33 PM, choonhong ang wrote:

> The district a is the baseline and we observe the difference between
> District a & b is not significant, we can choose to combine these 2
> values.
> How to write code to combine these 2 value ?
>
>> m1=glm(Claims~District+Group+Age+log(Holders),fami
>> ly=poisson,data=mydata)
>> summary(m1)
>
> Call:
> glm(formula = Claims ~ District + Group + Age + log(Holders),
> family = poisson, data = mydata)
>
> Deviance Residuals:
> Min 1Q Median 3Q Max
> -2.553115 -0.471819 0.002411 0.455274 1.800739
>
> Coefficients:
> Estimate Std. Error z value Pr(>|z|)
> (Intercept) -2.777752 0.689162 -4.031 5.56e-05 ***
> Districtb 0.119942 0.079861 1.502 0.133125
> Districtc 0.228371 0.144503 1.580 0.114019
> Districtd 0.571661 0.248792 2.298 0.021576 *
> Group>2l 0.794721 0.180354 4.406 1.05e-05 ***
> Group1-1.5l -0.003496 0.127947 -0.027 0.978202
> Group1.5-2l 0.379190 0.055856 6.789 1.13e-11 ***
> Age>35 -1.074971 0.389480 -2.760 0.005780 **
> Age25-29 -0.332131 0.129512 -2.564 0.010333 *
> Age30-35 -0.539815 0.160138 -3.371 0.000749 ***
> log(Holders) 1.201696 0.144135 8.337 < 2e-16 ***
> ---
> Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
>
> (Dispersion parameter for poisson family taken to be 1)
>
> Null deviance: 4236.68 on 63 degrees of freedom
> Residual deviance: 49.45 on 53 degrees of freedom
> AIC: 388.77
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