APA Dictionary of Psychology

an inferential test to determine whether a random sample comes from a population with a normal distribution. If the test statistic, W, is significant, then the null hypothesis that the distribution is normal should be rejected. Because so many of the most common statistical tests are designed for normally distributed data, Shapiro–Wilk is a useful test to identify those data sets that require a different approach. [Samuel S. Shapiro (1930–  ), U.S. statistician; Martin B. Wilk (1922–2013), Canadian-born U.S. statistician]