# Dictionary:Chi-square

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${\displaystyle \chi _{1}^{2}+\chi _{2}^{2}+\dots +\chi _{k}^{2}}$,
where ${\displaystyle \chi _{1},\chi _{2},\dots ,\chi _{k}}$ are independent, Gaussian, with zero mean, and with unit variance. The chi-square test is a statistical test of data distribution. If fi are observed, frequencies of occurrence and ei are the expected number of occurrences, the goodness of fit y is
${\displaystyle y=\sum {\frac {\left(f_{i}-e_{i}\right)^{2}}{e_{i}}}}$.