If the sample size is less than or equal to 2000 and you specify the NORMAL or NORMALTEST option in the PROC UNIVARIATE or PROC CAPABILITY statement, the Shapiro-Wilk W statistic is computed. Beginning with Version 7 of SAS, we have implemented improvements to our algorithm for computing W, therefore the statistic may be slightly different than in earlier versions. Since the distribution of W is highly skewed, small changes in W can result in large changes in its p-value.