[R] Ancova doesn't return test statistics

Marc Schwartz marc_schwartz at comcast.net
Thu Nov 15 17:02:27 CET 2007

On Thu, 2007-11-15 at 16:36 +0100, Johan A. Stenberg wrote:
> Dear all,
> I'm quite sure that this is a stupid question, but I'll ask anyway.
> I want to perform an ANCOVA with two continuous factors and three 
> categorical factors.
> Plant population growth rate (GR) = dependent variable
> Seed reduction due to herbivory (SR) = continuous explanatory variable
> Herbivore species (HS, 2 levels) = categorical explanatory variable
> Population (Pop, 24 levels) = categorical explanatory variable
> Population size (Popsize) = continuous explanatory variable
> Year (Year, 16 levels) = categorical explanatory variable
> My model is technically simple:
> model<-aov(GR~SR*HS*Pop*Popsize*Year)
> However, R is not returning any F and P values – only Df, Sum Sq and 
> Mean Sq. I have to remove either Year or Pop in order to get the test 
> statistics. Why is this?
> Thank you in advance!
> Johan A. Stenberg, Umea University, Sweden

See ?summary.aov which is referenced in the "See Also" section of ?aov
and is used in the examples therein.


Marc Schwartz

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