Cherilyn Young wrote:
> I have an itchy little question about the familiar Fisher's r to z
> transformation: The formula, expressed as z= sqrt (log e ( (1+r)/(1-r))),
> is in pretty much any older stats textbook. Does anyone know of a source
> where the equation is written to solve for r? I know it's a very uncommon
> use (if used at all in this way ), but I've got a very legitimate research
> need (and my brain's doing odd things when I'm trying to rewrite the
> equation).
r.back <- function(x)
{
((2.71828182845905^(2 * x)) - 1)/((2.71828182845905^(2 * x)) + 1)
}
fish.z <- function(x)
{
ifelse(x == 0, 0, 0.5 * log((1 + abs(x))/(1 - abs(x))) * (x/abs(x)))
}
Examples:
> fish.z(.45)
[1] 0.4847003
> r.back(.4847003)
[1] 0.45
> r.back(fish.z(.45))
[1] 0.45
HTH,
Chuck
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Chuck Cleland
Institute for the Study of Child Development
UMDNJ--Robert Wood Johnson Medical School
97 Paterson Street
New Brunswick, NJ 08903
phone: (732) 235-7699
fax: (732) 235-6189
http://www2.umdnj.edu/iscdweb/
http://members.nbci.com/cmcleland/
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