[R] Bootstrapping a repeated measures ANOVA

[Charles C. Berry]

On Fri, 16 Apr 2010, Fischer, Felix wrote:

> Hello everyone,
>
> i have a question regarding the sampling process in boot().

"PLEASE ... provide commented, minimal, self-contained, reproducible 
code." Which means something a correspondent could actually run.

But before that, a careful reading of

 	?boot

should get you started. Note these bits:

Arguments:

     data: The data as a vector, ...

    statistic: A function which when applied to data returns a vector
           containing the statistic(s) of interest.  When
           sim="parametric",	[snip]
 		  In all other cases
           statistic must take at least two arguments.  The first
           argument passed will always be the original data. The second
           will be a vector of indices, frequencies or weights which
           define the bootstrap sample. ...



HTH,

Chuck


>
> I try to bootstrap F-values for a repeated measures ANOVA to get a 
> confidence interval of F-values. Unfortunately, while the aov works 
> fine, it fails in the boot()-function. I think the problem might be that 
> the resampling process fails to select both lines of data representing 
> the 2 measuring times for one subject and I therefore get missing cases.
>
> The data is organised like this:
> subject ort        mz       PHQ
> 1          1          1          x
> 1          1          2          y
> 2          1          1          z
> 2          1          2          zz
> ...
>
>
> Is there any way to specify, that both lines need to be selected?
>
>
> Thanks a lot!
> Felix Fischer
>
> P.S. If you need to have a look to my code:
>
> F_values <- function(formula, data, indices) {
>    d <- data[indices,] # allows boot to select sample
>    fit=aov(formula,data=d) #fit model
>    return(c(summary(fit)[1][[1]][[1]]$`F value`, summary(fit)[2][[1]][[1]]$`F value`)) #return F-values
>   }
>
>   results <- boot(data=anova.daten, statistic=F_values,
>      R=10, formula=PHQ_Sum_score~mz*ort+Error(subject/mz))
>
>
> Dipl. Psych. Felix Fischer
>
> Medizinische Klinik mit Schwerpunkt Psychosomatik
> Charité -- Universitätsmedizin Berlin
> Luisenstr. 13a
> 10117 Berlin
>
> Tel.: 030 - 450 553575
> Email: felix.fischer at charite.de<mailto:felix.fischer at charite.de>
>
>
> 	[[alternative HTML version deleted]]
>
>

Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901