[R] Bootstrap Confidence Intervals

[_Fede_]

Hi again.

Watching this example that appears in the help page

ratio <- function(d, w) sum(d$x * w)/sum(d$u * w)
city.boot <- boot(city, ratio, R = 999, stype = "w",sim = "ordinary")
boot.ci(city.boot, conf = c(0.90,0.95),type =
c("norm","basic","perc","bca"))

I have tried to do the following (calling boot() to create an object to pass
to boot.ci):

x <- rnorm(20)
kurtosis <- function(x) (mean((x-mean(x))^4))/(sd(x)^4)
x.boot <- boot(x, kurtosis, R = 999, sim = "ordinary")
boot.ci(x.boot, conf = 0.95,type = c("norm","basic","perc","bca"))

But I don't know why this don't work. The editor window shows the following
error message:

Error in statistic(data, original, ...) : unused argument(s) (1:20)

I suppose that something is wrong with my data but I don't know what is.

Thanks in advance and wishing everybody a happy new year.

Regards 

_Fede_




Prof Brian Ripley wrote:
> 
> You need to call boot() to create an object to pass to boot.ci().
> 
> There are lots of examples in the help pages and in the book that package 
> 'boot' supports. From the help:
> 
> Usage:
> 
>       boot.ci(boot.out, conf = 0.95, type = "all",
>               index = 1:min(2,length(boot.out$t0)), var.t0 = NULL,
>               var.t = NULL, t0 = NULL, t = NULL, L = NULL, h = function(t)
> t,
>               hdot = function(t) rep(1,length(t)), hinv = function(t) t,
> ...)
> 
> Arguments:
> 
> boot.out: An object of class '"boot"' containing the output of a
>            bootstrap calculation.
> 
> and try class(z) .
> 
> 
> On Sun, 30 Dec 2007, _Fede_ wrote:
> 
>>
>>
>> Hi all.
>>
>> This is my first post in this forum. Finally I find a forum in the web
>> about
>> R, although is not in my language.
>>
>> Now I'm working with Bootstrap CI. I'd like to know how I can calculate a
>> Bootstrap CI for any statistic, in particular, for Kurtosis Coeficient. I
>> have done the following code lines:
>>
>>> library(boot)
>>> x=rnorm(20)
>>> kurtosis=function(x) (mean((x-mean(x))^4))/(sd(x)^4)
>>> z <- numeric(10000)
>>> for(i in 1:10000)
>>> z[i]=kurtosis(sample(x, replace=TRUE))
>>> boot.ci(z, conf = 0.95,type = c("norm","basic","perc","bca"))
>>
>> But the output shows the next error:
>>
>> Error en if (ncol(boot.out$t) < max(index)) { :
>>        argumento tiene longitud cero
>>
>> I don't know what is wrong.
>>
>> I hope that somebody can help me. Sorry for my english.
>>
>> All have a nice new year.
>>
>> _Fede_
>>
>>
> 
> -- 
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272866 (PA)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 
> 

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