Hi: On Sun, May 9, 2010 at 5:36 AM, Ravi Kulkarni <ravi.k...@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]] ______________________________________________ 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.
