Dale,
Other than the first SAS contrast, does the following demonstrate what
your asking for?
> summary(twoway)
material temp voltage
1:12 50:12 Min. : 20
2:12 65:12 1st Qu.: 70
3:12 80:12 Median :108
Mean :106
3rd Qu.:142
Max. :188
> contrasts(twoway$material)
2 3
1 0 0
2 1 0
3 0 1
> contrasts(twoway$temp)
65 80
50 0 0
65 1 0
80 0 1
> fit <- aov(voltage ~ material*temp, data=twoway)
> summary.aov(fit)
Df Sum Sq Mean Sq F value Pr(>F)
material 2 10684 5342 7.91 0.0020 **
temp 2 39119 19559 28.97 1.9e-07 ***
material:temp 4 9614 2403 3.56 0.0186 *
Residuals 27 18231 675
---
Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
# setting (partial) contrasts
> contrasts(twoway$material) <- c(1,-1,0) # ignoring the second
available df
> contrasts(twoway$temp) <- c(0,1,-1) # ignoring the second available df
> contrasts(twoway$material)
[,1] [,2]
1 1 -0.41
2 -1 -0.41
3 0 0.82
> contrasts(twoway$temp)
[,1] [,2]
50 0 -0.82
65 1 0.41
80 -1 0.41
> summary.aov(fit, split=list(material=list('m1-m2'=1), temp=list('t50 -
t80'=1)))
Df Sum Sq Mean Sq F value Pr(>F)
material 2 10684 5342 7.91 0.00198 **
material: m1-m2 1 3800 3800 5.63 0.02506 *
temp 2 39119 19559 28.97 1.9e-07 ***
temp: t50 - t80 1 11310 11310 16.75 0.00035 ***
material:temp 4 9614 2403 3.56 0.01861 *
material:temp: m1-m2.t50 - t80 1 4970 4970 7.36 0.01146 *
Residuals 27 18231 675
---
Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
# other examples of setting contrasts
# compare m1 vs m2 and m2 vs m3
> contrasts(twoway$material) <- matrix(c(1,-1,0,1,1,-2), nrow=3)
> contrasts(twoway$material)
[,1] [,2]
1 1 0
2 -1 1
3 0 -1
# compare m1 vs m2 and m1+m2 vs m3
> contrasts(twoway$material) <- matrix(c(1,-1,0,1,1,-2), nrow=3)
> contrasts(twoway$material)
[,1] [,2]
1 1 1
2 -1 1
3 0 -2
I'm not sure if 'summary.aov' is the only lm-family summary method with
the split argument.
DaveT.
*************************************
Silviculture Data Analyst
Ontario Forest Research Institute
Ontario Ministry of Natural Resources
[EMAIL PROTECTED]
http://ofri.mnr.gov.on.ca
*************************************
>-----Original Message-----
>From: Steele [mailto:[EMAIL PROTECTED]
>Sent: March 6, 2008 09:08 PM
>To: [EMAIL PROTECTED]
>Subject: [R] Finding Interaction and main effects contrasts
>for two-way ANOVA
>
>I've tried without success to calculate interaction and main effects
>contrasts using R. I've found the functions C(), contrasts(),
>se.contrasts() and fit.contrasts() in package gmodels. Given the url
>for a small dataset and the two-way anova model below, I'd like to
>reproduce the results from appended SAS code. Thanks. --Dale.
>
> ## the dataset (from Montgomery)
>twoway <- read.table("http://dsteele.veryspeedy.net/sta501/twoway.txt";,
>col.names=c('material', 'temp','voltage'),colClasses=c('factor',
>'factor', 'numeric'))
>
> ## the model
>fit <- aov(voltage ~ material*temp, data=twoway)
>
>/* SAS code */
>proc glm data=twoway;
>class material temp;
>model voltage = material temp material*temp;
>contrast '21-22-31+32' material*temp 0 0 0 1 -1 0 -1 1 0;
>estimate '21-22-31+32' material*temp 0 0 0 1 -1 0 -1 1 0;
>contrast 'material1-material2' material 1 -1 0;
>estimate 'material1-material2' material 1 -1 0;
>contrast 'temp50 - temp80' temp 1 0 -1;
>estimate 'temp50 - temp80' temp 1 0 -1;
>run;
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
