[R] Problem with Loops
Erik Iverson
eriki at ccbr.umn.edu
Fri Apr 9 05:28:49 CEST 2010
Hello,
mtesche wrote:
> Hello,
>
> I am trying to write a script with the end goal of graphing power (y) as a
> result of sample size (x) at a variety of effects sizes. I am new to loops,
> and I think my problem is there. Here's the script, which is modified from
> the script found at the bootom of
> http://www.statmethods.net/stats/power.html. ANy help would be much
> appreciated!mtesche at ualberta.ca
>
> library(pwr)
> library(lattice)
>
> # range of sample sizes
> r <- seq(5,300,5)
> nr <- length(r)
>
> # effect sizes
> p <- seq(.4,1.2,.2)
> np <- length(p)
>
> # obtain power
> power <- array(numeric(nr*np), dim=c(nr,np))
> for (i in 1:np){
> for (j in 1:nr){
> result <- pwr.t.test(n = r[j], d = p[i],
> sig.level = .05, power = NULL,
> alternative = "two.sided")
> power[j,i] <- ceiling(result$power)
> }
> }
First problem. Why are you calling ceiling, which will return 1 for any value
of a power? What were you thinking that line was doing?
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