Well, since we don't have Data.txt it is kind of hard for us to replicate what you have done.
Here goes a guess as to what the problem may be. Have you told R anywhere that S1 and S2 are factors with 6 levels rather than numeric vectors? Or are you just hoping that the computer can read your mind to find out this information? (reading minds is one of the things that R and computers in general are not very good at yet. I have made a note to my future self to use the TimeTravel package to send a copy of the ESP package back to my past self, but I have not received it yet). -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.s...@imail.org 801.408.8111 > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r- > project.org] On Behalf Of Lars Bergemann > Sent: Wednesday, July 08, 2009 8:35 AM > To: r-help@r-project.org > Subject: [R] Two-way ANOVA gives different results using anova(lm()) > than doing it by hand > > > Hey! > > > > Could you please take a quick look at what I have done? Somehow I get > wrong results using the anova(lm()) combination compared to doing a two > way ANOVA by hand. > > > > Running: > > > > Data<-read.table("Data.txt"); > g<-lm(ExM~S1*S2,Data); > anova(g); > > > > Gives: > > > > Analysis of Variance Table > > Response: ExM > Df Sum Sq Mean Sq F value Pr(>F) > S1 1 4.3679 4.3679 167.045 < 2.2e-16 *** > S2 1 0.9427 0.9427 36.053 8.236e-09 *** > S1:S2 1 0.3231 0.3231 12.357 0.0005371 *** > Residuals 212 5.5434 0.0261 > > > I compared it to the work done by hand, ie calculated all the different > square sums using sum() and tapply(). > > So I know that anova(lm()) gets the degrees of freedom equal two 1, 1, > 1 and 212 when it should be 5, 5, 25 and 180. Also, the square sums are > quite different ... I get 4.xx, 4.xx, 1.xx, 0.xx ... as you see, what > anova(lm()) gets is different. > > > > The data: S1 has 6 levels, so has S2. On average, each cell has 6 > values, most cells have actually 6 values, and there are two of each: > 5, 7, 4, 8 - so average 6. > > > > Could you please help me, why it does not work with anova(lm())? I > tried quite a few thinks found with Google, but it all gave me the same > result as anova(lm()) ... > > > > Thanks a lot! > > > > Lars > > _________________________________________________________________ > > ______________________________________________ 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.
