An indication of the amount of skewness of a distribution and its direction. The formula for SK is:
SK = 3(mean-median)/standard deviation
A positive SK indicates that the Mean of the data set is larger than the Median, or that the data set is skewed right. Conversely, a negative SK indicates that the Mean of the data set is smaller than the Median, or that the distribution is skewed left.
Reference: Kiemele, Mark J., Schmidt, Stephen R., and Berdine, Ronald J. (2000). Basic Statistics for Continuous Improvement. Colorado Springs, CO: Air Academy Press. pp.2-64 - 2-65.