any procedure used to test whether a data set follows a normal distribution. Many statistical procedures are based on the assumption that the random variable of interest is normally distributed. When this assumption is violated, interpretation and inference from the statistical tests may not be warranted. Often, normality is most conveniently assessed using graphical methods, such as a stem-and-leaf plot, to visualize the differences between an empirical distribution and the standard normal distribution. Alternatively, there are statistical tests of normality, such as the Kolmogorov–Smirnov goodness-of-fit test and the Shapiro–Wilk test.