[R] question about anova() output

[Robert Burrows]

Hello,

I am getting output from anova() and summary(aov()) that depends on the
order of the factors in the fitted model object, and this has me baffled. I
see this dependency with the data.frame below but not with an example (table
6.4) from Montgomery's DOE book. This is with R 1.3.0 on Debian GNU-Linux.

Where have I gone wrong?

> centerpts
    run sample CH50mg
1  day1 dev126   0.56
2  day1 dev126   0.70
3  day1 dev126   0.82
4  day1 dev126   0.72
5  day2 dev126   0.57
6  day2 dev126   0.60
7  day3 dev126   0.61
8  day3 dev126   0.64
9  day3 dev126   0.68
10 day3 dev126   0.68
11 day1 dev118   0.77
12 day1 dev118   0.80
13 day1 dev118   0.86
14 day2 dev118   0.71
15 day2 dev118   0.70
16 day3 dev118   0.77
17 day3 dev118   0.77
18 day3 dev118   0.77
19 day3 dev118   0.80
20 day1 rgf108   0.77
21 day1 rgf108   0.86
22 day1 rgf108   0.82
23 day2 rgf108   0.62
24 day2 rgf108   0.63
25 day3 rgf108   0.66
26 day3 rgf108   0.71
27 day3 rgf108   0.69
28 day3 rgf108   0.69
>
>
> anova(lm(CH50mg~run+sample+run*sample,data=centerpts))
Analysis of Variance Table

Response: CH50mg
           Df   Sum Sq  Mean Sq F value    Pr(>F)
run         2 0.064308 0.032154 12.5597 0.0003343
sample      2 0.068649 0.034324 13.4075 0.0002337
run:sample  4 0.010444 0.002611  1.0199 0.4221699
Residuals  19 0.048642 0.002560
>
>
> anova(lm(CH50mg~sample+run+run*sample,data=centerpts))
Analysis of Variance Table

Response: CH50mg
           Df   Sum Sq  Mean Sq F value    Pr(>F)
sample      2 0.061927 0.030964 12.0948 0.0004093
run         2 0.071029 0.035515 13.8725 0.0001931
sample:run  4 0.010444 0.002611  1.0199 0.4221699
Residuals  19 0.048642 0.002560

TIA,

-- 
Robert Burrows
New England Biometrics
rbb at nebiometrics.com



-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._