# Chi-square test

A chi-square test is any statistical hypothesis test in which the test statistic has a chi-square distribution if the null hypothesis is true. These include:

All such tests involve a statistic of the form

[itex]X^2=\sum\frac{(\mathrm{observed}-\mathrm{expected})^2}{\mathrm{expected}},[itex]

where the word "expected" often does not denote an expected value, but an observable estimate of an expected value.

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