I omit to precise that I already try to generate data based on the mean and
sd of two variables.

x=rnorm(20,1,5)+1:20

y=rnorm(20,1,7)+41:60

simu<-function(x,y,n) {
    simu=vector("list",length=n)

    for(i in 1:n) {

        x=c(x,rnorm(1,mean(x),sd(x)))
        y=c(y,rnorm(1,mean(y),sd(y)))

        simu[[i]]$x<-x
        simu[[i]]$y<-y


    }

    return(simu)
}

test=simu(x,y,60)
lapply(test, function(x) cor.test(x$x,x$y))

As you could see, the correlation is disappearing with increasing N.
Perhaps, a bootstrap with lm or cor.test could solve my problem.



2012/3/13 guillaume chaumet <guillaumechaumet@gmail.com>

> Dear R list,
> I have a population with two groups. I want to simulate an gradually
> increase of the number of subjects for group 1 based on mean and sd of two
> variables (correlated).
> Bootstrap ?
> Sample ?
> Simulation ? (
>
> I just search some clues.
> Thank you
>
> Guillaume
>
>
>

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