[R] CORDIF test

[Ista Zahn]

Hi Elizabeth,

In addition to the helpful suggestions you have already received, I
would add that for simple functions like this it can be very
instructive to just look at the function definition. Loading the
multilevel package and typing 'cordif' will show you

function (rvalue1, rvalue2, n1, n2)
{
    zvalue1 <- 0.5 * ((log(1 + rvalue1)) - (log(1 - rvalue1)))
    zvalue2 <- 0.5 * ((log(1 + rvalue2)) - (log(1 - rvalue2)))
    zest <- (zvalue1 - zvalue2)/sqrt(1/(n1 - 3) + 1/(n2 - 3))
    out <- list(`z value` = zest)
    return(out)
}


best.
Ista

On Wed, Apr 2, 2014 at 9:09 AM, Elizabeth Caron-Gamache
<babeth_013 at icloud.com> wrote:
> Hi,
>
> I search on your website for a definition of the CORDIF test, but it wasn’t successful. I’m analyzing an article that use that test and it’s not really documented on the net. The article refers to your website, so I pretend that you will be able to give me a brief explanation of this test. Here is the cote that talk about this test in my article :
>
> ‘' To compare these regressions and to see which—either body height or LLL—is best related to performance (Pearson correlation coefficients comparison), a CORDIF test (R software [www.r-project.org], multilevel package, ver- sion 2.12.1) was performed.
>
> Does it use parametric or non-parametric values ?
> Is it a test to compare 2 groups only or it can be used for a comparison of more than two groups ?
> Why is it so hard to find information on that test on the net ?
>
> Thanks for your time
> Have a nice day
>
> Elizabeth Caron
> Physical therapist student, Laval University, Qc, Canada
>
>
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