R help - Apr 2008 - Power curve for a wilcoxon test

Hi,
I am trying to write R code to produce a power curve to show how the power of a 
Wilcoxon-test varies depending on the mean, with data generated from a uniform
distribution. Any ideas how I should go about this?Louisa
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Louisa Hay <louisahay <at> msn.com> writes:
> 
> 
> Hi,
> I am trying to write R code to produce a power curve to show 
> how the power of a 
> Wilcoxon-test varies depending on the mean, with data 
> generated from a uniform
> distribution. Any ideas
> how I should go about this?Louisa
  Here's a brute-force approach that
seems to work reasonably well.  Adapt to 
suit yourself ...

wilcox.pval <- function(m2,m1=0,n=20) {
    x1 <- runif(n,m1-0.5,m1+0.5)
    x2 <- runif(n,m2-0.5,m2+0.5)
    wilcox.test(x1,x2)$p.value
}

wilcox.pow <- function(m2,m1=0,n=20, alpha=0.05, N=500) {
    pvals <- replicate(N,wilcox.pval(m2,m1,n))
    sum(pvals<alpha)/N
}

mvec <- seq(0,0.5,by=0.05)
powvec <- sapply(mvec,wilcox.pow)

plot(mvec,powvec)

On 4/14/2008 8:59 AM, Louisa Hay wrote:
> Hi,
> I am trying to write R code to produce a power curve to show how the power
of a
> Wilcoxon-test varies depending on the mean, with data generated from a
uniform distribution. Any ideas how I should go about this?Louisa
I think I gave you enough of a hint to do this one in my previous 
response to you.  Did you read it?

(Are we doing your homework for you?)

Duncan Murdoch