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
Charit? -- Universit?tsmedizin Berlin
Luisenstr. 13a
10117 Berlin
Tel.: 030 - 450 553575
Email: felix.fisc...@charite.de<mailto:felix.fisc...@charite.de>
[[alternative HTML version deleted]]
Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:cbe...@tajo.ucsd.edu UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
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