The same method for estimating skewness is used in SAS and SPSS. Missing values
(NA) are stripped before the computation. Note that at least 3 observations
are needed to compute skewness.
References
Rasch, D., Kubinger, K. D., & Yanagida, T. (2011). Statistics in psychology
- Using R and SPSS. New York: John Wiley & Sons.