Different results

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vasilis pappas <vasileios_p at yahoo.gr> writes:
Hello everybody,
   I've been practicing with some data in R and SPSS and I noticed that there are some differences in ANOVA results.

For example with :
y<-c(1,2,34,2,3,45,2,1,67,3,2,67,2,2,98,4,4,23,1,1,23,2,3,45) and
x<-rep(c(1,2,3),8)

   I get in R ( with summary(aov(y~x)) )
MSres=350.7
df=22

   while in SPSS I get
MSres=221.9
df=21

Can enyone explain me what is the problem or what am I doing wrong?
You need  x <- factor(x) , I guess.
O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907

Hello everybody,
   I've been practicing with some data in R and SPSS and I noticed that there are some differences in ANOVA results.

For example with :
y<-c(1,2,34,2,3,45,2,1,67,3,2,67,2,2,98,4,4,23,1,1,23,2,3,45) and
x<-rep(c(1,2,3),8)

   I get in R ( with summary(aov(y~x)) )
MSres=350.7
df=22

   while in SPSS I get
MSres=221.9
df=21

Can enyone explain me what is the problem or what am I doing wrong?
If you want to do a traditional one-way anova, you have to declare x
to be a factor:
y<-c(1,2,34,2,3,45,2,1,67,3,2,67,2,2,98,4,4,23,1,1,23,2,3,45)
x<-rep(c(1,2,3),8)
summary(aov(y~x))
Df Sum Sq Mean Sq F value    Pr(>F)    
x            1 9264.1  9264.1  26.414 3.761e-05 ***
Residuals   22 7715.9   350.7                      
---
Signif. codes:  0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1
xf<-as.factor(x)
summary(aov(y~xf))
Df  Sum Sq Mean Sq F value    Pr(>F)    
xf           2 12320.1  6160.0  27.761 1.269e-06 ***
Residuals   21  4659.9   221.9                      
---
Signif. codes:  0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1 

Notice that when x is not a factor there is only one degree of freedom for 
x.

David Scott

_________________________________________________________________
David Scott	Department of Statistics, Tamaki Campus
		The University of Auckland, PB 92019
		Auckland	NEW ZEALAND
Phone: +64 9 373 7599 ext 86830		Fax: +64 9 373 7000
Email:	d.scott at auckland.ac.nz 

Graduate Officer, Department of Statistics
x is numeric, so R consider this to be a linear regression, not a 3 group analysis. To do the latter in R:

x<-factor(1:3)

Read the R Introductory manuals or the first few and other relevant chapters Venables' and Ripley's MASS first, please!

-- Bert Gunter

Hello everybody,
   I've been practicing with some data in R and SPSS and I noticed that there are some differences in ANOVA results.

For example with :
y<-c(1,2,34,2,3,45,2,1,67,3,2,67,2,2,98,4,4,23,1,1,23,2,3,45) and
x<-rep(c(1,2,3),8)

   I get in R ( with summary(aov(y~x)) )
MSres=350.7
df=22

   while in SPSS I get
MSres=221.9
df=21

Can enyone explain me what is the problem or what am I doing wrong?
                         Thanks for your interest a priori,
                                                                       Vasileios.

---------------------------------

????????????????? ?????? ???????????? ??????@yahoo.gr

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