Forcing integers to be nominal

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?

-Tim

-- 
Tim Wilson      |   Visit Sibley online:   | Check out:
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