On Thu, 27 May 2004, [iso-8859-7] vasilis pappas wrote:
> 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: [EMAIL PROTECTED]
Graduate Officer, Department of Statistics
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