A cautionary note on the use of the Kolmogorov-Smirnov test for normality

The Kolmogorov-Smirnov goodness-of-fit test is used in many applications for testing normality in climate research. This note shows that the test usually leads to systematic and drastic errors. When the mean and the standard deviation are estimated, it is much too conservative in the sense that its p values are strongly biased upward. One may think that this is a small sample problem, but it is not. There is a correction of the Kolmogorov-Smirnov test by Lilliefors, which is in fact sometimes confused with the original Kolmogorov-Smirnov test. Both the Jarque-Bera and the Shapiro-Wilk tests for normality are good alternatives to the Kolmogorov-Smirnov test. A power comparison of eight different tests has been undertaken, favoring the Jarque-Bera and the Shapiro-Wilk tests. The Jarque-Bera and the Kolmogorov-Smirnov tests are also applied to a monthly mean dataset of geopotential height at 500 hPa. The two tests give very different results and illustrate the danger of using the Kolmogorov-Smirnov test.