Dear all,
I was trying to do some contrasts within ANOVA. I searched the archive and
found a clue posted by Steffen Katzner
( http://tolstoy.newcastle.edu.au/R/help/06/01/19385.html)
I have three levels for a factor names "StdLot". I just want to make three
comparisons, 1 vs 2, 1 vs 3 and 2 vs 3.
First,
contrasts(d3$StdLot,3)<-matrix(c(1,-1, 0,0,1,-1,1,0,-1),3,3) #d3 is the
data set. set up the contrast matrix
Second,
aov(Bkg~StdLot,na.rm=T,data=d3,contrasts=contrasts(d3$StdLot))->mod.aov
#ANOVA,
Finally,
summary(mod.aov,split=list(StdLot=list('1 vs 2'=1,'2 vs 3'=2,'1 vs 3'=3)))
#comparison summary
Here is the final result I got, the third comparison is missing. Does anyone
have any idea what is wrong here? If I change the order of the comparisons
it's always the third one missing. So I guess it's not due to the data.
Appreciate any comment.
Df Sum Sq Mean Sq F value Pr(>F)
StdLot 2 1.905 0.953 10.3769 3.710e-05 ***
StdLot: 1 vs 2 1 0.223 0.223 2.4239 0.1200
StdLot: 2 vs 3 1 1.683 1.683 18.3299 2.162e-05 ***
StdLot: 1 vs 3 1
Residuals 601 55.173 0.092
---
Signif. codes: 0 *** 0.001 ** 0.01 * 0.05 . 0.1 1
2 observations deleted due to missingness
--
Jun Shen PhD
PK/PD Scientist
BioPharma Services
Millipore Corporation
15 Research Park Dr.
St Charles, MO 63304
Direct: 636-720-1589
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