[R] F values from a Repeated Measures aov

From: Alex Baugh <alex.baugh_at_gmail.com>
Date: Mon, 28 Apr 2008 16:58:30 -0500


Hi Folks,

I have repeated measures for data on association time (under 2 acoustic condtions) in male and female frogs as they grow to adulthood (6 timepoints). Thus, two within-subject variables (Acoustic Condition: 2 levels, Timepoint: 6 levels) and one between-subject variable (Sex:male or female).

I am pretty sure my distributions depart from normality but I would first like to simply run a RM anova on the data. My problem is that when I do this I generate different values of F for my main effects and interaction when I do the analysis in [R] and SPSS - so I don't know which one to believe.

Here is my code in R:

>mydata.tab=read.delim("mydata.txt", header=T) #read in my data

>mydata.tab$Timepoint=as.factor(mydata.tab$Timepoint) #col headings
are factors so df are correct

>mydata.tab$Acx.Cond=as.factor(mydata.tab$Acx.Cond)

>mydata.tab$Sex=as.factor(mydata.tab$Sex)

> aov.F=aov(Targ.Assoc.Time~(Timepoint*Acx.Cond*Sex) + Error(Subject/(Timepoint*Acx.Cond))+(Sex), data=mydata.tab)

#run aov where i look at the main effects of Timepoint, Acoustic Condition and Sex as well as all the interactions therein on the amount of time a frog spends associating with the target sound. Include anything to do with Subject in the error term.

Does this look right for a Repeated Measures ANOVA, or am I missing something to make it RM and that explains the large discrepancies in my F-values between [R] and SPSS?

As soon as I get this canonical aov code figured out I want to derive my p-values by bootstrapping my F distributions, but first I need those canonical F's.

Thanks
-Alex

-- 
Alexander T Baugh
Section of Integrative Biology
Univ. of Texas at Austin C0930
Austin, TX 78712
http://darktropic.blogspot.com/

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Received on Mon 28 Apr 2008 - 22:11:52 GMT

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