Skewness: McNemar, Q. Psychological Statistics. Fourth edition. New York: Wiley 1969. p. 25
Critical ratio of skewness: Snedecor, G. W., and Cochran, W. G. Statistical Methods. Sixth edition. Ames, lowa: The lowa State University Press, 1967. p. 86
Table for testing skewness: Snedecor, G. W., and Cochran, W. G. Statistical Methods. Sixth edition. Ames, lowa: The lowa State University Press, 1967. p. 552
SAS: UNIVARIATE, MEANS