Kolmogorov-Smirnov Test
The Kolmogorov-Smirnov test is a widely used, non-parametric statistical test for assessing whether two data sets come from a single population or from different populations. The name of the test arose from the surnames of its creators, Russian mathematician Andrey Kolmogorov and his compatriot, mathematician and physicist Nikolai Smirnov. Kolmogorov-Smirnov test is a powerful and general technique that has applications in many different fields.
The test is used to determine if two samples drawn from an unknown distribution come from the same population. A Kolmogorov-Smirnov test is used when the data are continuous; when the data are categorical, the chi-square test is used. The Kolmogorov-Smirnov test may be used to determine if two samples come from populations that have a common distribution. This test is based on the empirical cumulative distribution functions (ECDFs) of the two samples and uses these sample functions to reject the null hypothesis that the two populations have the same distribution.
In the classical Kolmogorov-Smirnov test, the two samples are assumed to come from the same underlying distribution, and the null hypothesis is that the two samples come from the same population. The test statistic is used to assess the fit of the observed distribution to the assumed distribution. The test statistic is the maximum absolute distance (or discrepency) between the two empirical cumulative distribution functions (or CDFs). A hierarchical decision rule is used to determine the significance of the test statistic.
To perform the Kolmogorov-Smirnov test, the two samples must be selected and the test statistic must be calculated. The test statistic is calculated as the maximum of the absolute differences between the empirical CDFs of the two samples (the gap between the lines of the empirical CDFs). Then the test statistic must be compared to a table of critical values; if the observed test statistic is greater than the critical value, the null hypothesis is rejected.
The Kolmogorov-Smirnov test is a powerful and robust nonparametric test for checking for differences between two samples. It can be used to test whether samples drawn from the same population have different distributions, or whether samples come from different populations. The test is relatively easy to implement, and can provide powerful insight into the underlying distribution of a data set. In addition, this test can be used in many different fields including biological and medical research, environmental studies, and social sciences. The Kolmogorov-Smirnov test can be used to compare observational and experimental data, or to compare data from different groups or populations.