[R] Forcing integers to be nominal

[John Fox]

Dear Tim,

As has been pointed out, you need to ensure that YearColl is coerced to a 
factor. The read.spss function by default converts variables to factors 
when they have value labels in the SPSS data set; otherwise numeric 
variables without value labels remain numeric. See help(read.spss).

I hope that this helps,
  John

At 02:10 AM 8/7/2002 -0500, Tim Wilson wrote:
>Hi everyone,
>
>I've got a problem with an analysis of variance where it appears that my
>independent variable is being treated as an integer when it should be
>nominal.
>
>The data are being loaded from an SPSS file and the independent variable
>'YearColl' corresponds (surprisingly enough) to a student's year in
>college. :-) The integers 1-4 are used in the dataset for this purpose.
>My quick little anova gives this result:
>
> > mir.aov <- aov(DepressT ~ YearColl, data=mir)
> > summary(mir.aov)
>              Df  Sum Sq Mean Sq F value   Pr(>F)
>YearColl      1   955.7   955.7  10.305 0.001474 **
>Residuals   293 27172.5    92.7
>---
>Signif. codes:  0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1
>
>I was expecting the df for YearColl to be (k-1) = 3.
>
>Am I reading this right? Is there a way to force integers to act like
>nominal data?


-----------------------------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: jfox at mcmaster.ca
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox
-----------------------------------------------------

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