In probability theory and statistics, the chi-square distribution (also chi-squared or distribution) is one of the most widely used theoreticalprobability distributions. Chi-square distribution with degrees of freedom is written as .[1] It is a special case of gamma distribution.[2]
Chi-square distribution is primarily used in statistical significance tests and confidence intervals.[3] It is useful, because it is relatively easy to show that certain probability distributions come close to it, under certain conditions. One of these conditions is that the null hypothesis must be true. Another one is that the different random variables (or observations) must be independent of each other.