[R] trouble using boot package

[Angelo Canty]

Please read the help file!

mean is not a valid statistic to boot.

mean.boot <- function(x, i) mean(x[i])

is valid.

You can easily return as many values from boot as you like.
For example

mean.boot1 <- function(x, i)
    tapply(x$StomWt[i], list(x$Age, x$Quarter)

Of course if you want to do this, you need to use a stratified
bootstrap using the strata argument to boot
strata=tapply(d2$StomWt, list(d2$Age, d2$Quarter)) should work.

Angelo Canty

On Fri, 25 Jun 2004, Louize Hill wrote:

> Hello,
> 
> I am trying to carry out a bootstrap analysis (using the boot package) on a
> table and cannot work out how to get the results I need!
> I have a table ("d2") with 4 columns: "ID_code", "Age", "Quarter" and
> "StomWt". Age (0-5) and Quarter (1-4) are my strata
> Therefore I wish to estimate the confidence intervals for the mean StomWt
> for each Age and Quarter.
> 
> If I do this manually for each age / quarter I get the following:
> 
> > boot (d2$StomWt[d2$Age=="0" & d2$Quarter=="1"], mean, R=999)
> 
> ORDINARY NONPARAMETRIC BOOTSTRAP
> 
> Call:
> boot(data = d2$StomWt[d2$Age == "0" & d2$Quarter == "1"], statistic = mean,
>     R = 999)
> 
> Bootstrap Statistics :
>     original  bias    std. error
> t1*    3.365       0           0
> 
> Firstly - shouldn't the bias and std error be something other than 0?
> Furthermore, I would like to know if there is a way (function?) I can use
> that would automate this?
> 
> Thank you for your help
> Louize Hill
> 
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> 

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