Hi:

On Sun, May 9, 2010 at 5:36 AM, Ravi Kulkarni <ravi.kulk@gmail.com> wrote:

>
> I notice something curious about how aov() treats a numeric factor:
>
> "score" is a dependent variable and "group" is a factor in a one-way ANOVA.
> But "group" contains numeric codes and is not a factor (checked with
> is.factor). An ANOVA done using:
>
> > aov(score~factor(group), data=mydata)
>
> gives the right answers. But
>
> > aov(score~group, data=mydata)
>
> also produces an ANOVA table, with incorrect entries. My question is: what
> exactly is R doing when I did not specify that "group" was a factor?
>

It's doing simple linear regression, because group is evidently a numeric
variable
in mydata. Type

str(mydata)

to see what you've got. R cannot divine whether you want an ANOVA in this
problem or simple linear regression. In a model with one variable on the RHS
of
the model formula, R will perform regression if it is numeric and ANOVA if
it is
a factor; it is up to you to know the type of variables you are inputting
into a
model. str() is one of the most useful and important functions in R; it
would benefit
you to acquaint yourself with its features.

HTH,
Dennis

>
> Ravi Kulkarni
> --
> View this message in context:
> http://r.789695.n4.nabble.com/Question-about-factor-that-is-numeric-in-aov-tp2164393p2164393.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> 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.
>

	[[alternative HTML version deleted]]

