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# logit transformation of proportion or percent (J. Fox)
# last modified 2012-06-24 by J. Fox
logit <- function(p, percents=range.p[2] > 1, adjust){
range.p <- range(p, na.rm=TRUE)
if (percents){
if (range.p[1] < 0 || range.p[1] > 100) stop("p must be in the range 0 to 100")
p <- p/100
range.p <- range.p/100
}
else if (range.p[1] < 0 || range.p[1] > 1) stop("p must be in the range 0 to 1")
a <-if (missing(adjust)) {
if (isTRUE(all.equal(range.p[1], 0)) || isTRUE(all.equal(range.p[2], 1))) .025 else 0
}
else adjust
if (missing(adjust) && a != 0) warning(paste("proportions remapped to (", a, ", ", 1-a, ")", sep=""))
a <- 1 - 2*a
log((0.50 + a*(p - 0.50))/(1 - (0.50 + a*(p - 0.50))))
}
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