# Dictionary:Chi-square

(kī) A quantity distributed as

where are independent, Gaussian, with zero mean, and with unit variance. The chi-square test is a statistical test of data distribution. If *f*_{i} are observed, frequencies of occurrence and *e*_{i} are the expected number of occurrences, the **goodness of fit** *y* is

The goodness of fit can be related (by the use of tables) to the probability that the observed data fit the model with the assumed number of degrees of freedom.