[R] skewness, kurtosis

[Wolfgang Koller]

Dear R-Users and Developpers,

Currently R does not include functions to compute the skewness and 
kurtosis. I programmed it myself in the following way, but probably 
*real* programmers/statisticians can do that better:
 
mykurtosis <- function(x) {  
m4 <- mean((x-mean(x))^4) 
kurt <- m4/(sd(x)^4)-3  
kurt
}

myskewness <-  function(x) {
m3 <- mean((x-mean(x))^3)
skew <- m3/(sd(x)^3)
skew
}

I would also suggest to include the quartile-coefficient of skewness 
(sorry if this translation from German is not correct). This measure 
is confined to the interval [0,1] and much easier to interpret. 
My try:

myqcskewness <-  function(x) {
  x25 <- as.double(quantile(x,prob=0.25))
  x75 <- as.double(quantile(x,prob=0.75))
  qcsk <- (x25+x75-2*mean(x))/(x75-x25)
  qcsk
}

Finally a question which actually is not R-related (please excuse 
this misuse of the list):
Is there something like a "quantile-coefficient of kurtosis"??
 Maybe:
k = (2b-a)/a  with   a = x_{p} - x_{1-p},   b = x_{q} - x_{1-q},
x_{} are quantiles, and p and q are chosen so that k=0 for the normal 
distribution.

Thanks for help!!

WK


----------------------------------------------------------
Wolfgang Koller,  koller2 at fgr.wu-wien.ac.at
Research Institute for European Affairs
Vienna University of Economics and Business Administration
Althanstrasse 39-45, 1090 Vienna, Austria
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._