#' Moment coefficient of skewness
#'
#' @description
#' Compute the moment coefficient of skewness of a continuous, possibly non-normal variable.
#'
#' @param x Numeric vector, the values of the variable of interest.
#'
#' @return
#' A numerical value: the moment coefficient of skewness of `x`.
#'
#' @author Alessandro Samuel-Rosa \email{alessandrosamuelrosa@@gmail.com}
#'
#' @references
#' B. S. Everitt, _The Cambridge Dictionary of Statistics_, 3rd ed. Cambridge: Cambridge University
#' Press, 2006, p. 432.
#'
#' D. N. Joanes and C. A. Gill, Comparing measures of sample skewness and kurtosis, _J Royal
#' Statistical Soc D_, vol. 47, no. 1, pp. 183–189, Mar. 1998, doi: 10.1111/1467-9884.00122.
#'
#' H. Cramér, _Mathematical Methods of Statistics_. Princeton: Princeton University Press, 1946,
#' p. 575.
#'
#' @examples
#' x <- rlnorm(10)
#' skw <- skewness(x)
# FUNCTION #########################################################################################
#' @export
skewness <-
function(x) {
# Check function arguments
if (!is.numeric(x)) {
stop("'x' should be a numeric vector")
}
# Compute the moment coefficient of skewness
n <- length(x)
mean_x <- mean(x)
mean_second_moment <- sum((x - mean_x)^2) / n
mean_third_moment <- sum((x - mean_x)^3) / n
skewness <- mean_third_moment / mean_second_moment^1.5
return(skewness)
}
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