parameters.johnson.su <- function(z
,quantile.neg.3z
,quantile.neg.z
,quantile.z
,quantile.3z) {
ret <- list()
est.m <- quantile.3z - quantile.z
est.n <- quantile.neg.z - quantile.neg.3z
est.p <- quantile.z - quantile.neg.z
#Johnson SU parameter estimates (Slifker/Shapiro 1980)
ret$eta <- 2*z / acosh(.5*(est.m/est.p + est.n/est.p))
ret$gamma <- ret$eta*asinh(
(est.n / est.p - est.m / est.p) /
(2*sqrt( (est.m/est.p)*(est.n/est.p) -1 ) )
)
ret$lambda <- (2*est.p*sqrt( (est.m/est.p)*(est.n/est.p) -1 ) /
( (est.m/est.p +est.n /est.p -2 ) *sqrt((est.m/est.p +est.n /est.p +2 )))
)
ret$epsilon <- ((quantile.z +quantile.neg.z)/2 +
est.p*(est.n/est.p -est.m/est.p) / ( 2*(est.m/est.p +est.n/est.p -2) )
)
ret$m <- est.m
ret$n <- est.n
ret$p <- est.p
ret
}
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