[S] anova drops off variables

W. Keith Moser (4ester@compuserve.com)
Wed, 27 May 1998 15:10:22 -0400


S-Newsers

I have a ridiculously simple question, but I cannot find the answer in the
S-plus 4.5 documentation.

I have a data set where I am examining the percent cover of particular
species of plants. I have categorical variables (cmpt, numgrowbrn,
lastburn, season) and numerical variables (basum).

I ran two anovas:

> arst.aov <- aov(arst ~ cmpt + basum + numgrowbrn + season + lastburn,
na.action = na.omit)
> anova(arst.aov)
Analysis of Variance Table

Response: arst

Terms added sequentially (first to last)
Df Sum of Sq Mean Sq F Value Pr(F)
cmpt 5 179.420 35.88396 1.639962 0.1531631
basum 1 48.415 48.41475 2.212641 0.1390859
Residuals 143 3128.979 21.88098
> arst.nocmpt.aov <- aov(arst ~ basum + numgrowbrn + season + lastburn,
na.action = na.omit)
> anova(arst.nocmpt.aov)
Analysis of Variance Table

Response: arst

Terms added sequentially (first to last)
Df Sum of Sq Mean Sq F Value Pr(F)
basum 1 16.799 16.79910 0.753463 0.3868164
numgrowbrn 1 43.061 43.06106 1.931348 0.1667411
season 1 62.069 62.06851 2.783858 0.0973765
lastburn 1 1.986 1.98568 0.089061 0.7658021
Residuals 145 3232.900 22.29586

QUESTION: Why did the first anova drop off numgrowbrn, season and
lastburn?

Thank you inn advance.

Keith
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