Skewness and kurtosis values in descriptives

Comments

• RaviSelker

  May 2016 edited 4:23PM

  This is how we calculate skewness and kurtosis:

  .descriptivesKurtosis <- function(x) {
  
      # Kurtosis function as in SPSS: 
      # http://www.ats.ucla.edu/stat/mult_pkg/faq/general/kurtosis.htm
      # http://en.wikipedia.org/wiki/Kurtosis#Estimators_of_population_kurtosis
  
      n <- length(x)
      s4 <- sum((x - mean(x))^4)
      s2 <- sum((x - mean(x))^2)
      v <- s2 / (n-1)
      a <- (n * (n + 1)) / ((n - 1) * (n - 2) * (n - 3))
      b <- s4 / (v^2)
      c <- (-3 * (n - 1)^2) / ((n - 2) * (n - 3))
      kurtosis <- a * b + c
      return(kurtosis)
  }
  
  .descriptivesSkewness <- function(x) {
  
      # Skewness function as in SPSS (for samples spaces): 
      # http://suite101.com/article/skew-and-how-skewness-is-calculated-in-statistical-software-a231005
  
      n <- length(x)
      m <- mean(x)
      s <- sd(x) 
      z <- (x - m) / s  # z scores
      a <- n / ((n - 1) * (n - 2))
      skewness <- sum(z^3) * a
      return(skewness)
  }
  

  I'm not sure how the R package calculates these statistics. Could you attach the csv you are using to calculate these statistics so I can check it?