Why “goodness of fit”? This name suggests that the statistic addresses the question of how well or “good” a set of data “fits” an existing set. The set of data is, of course, what you observe. The “fit” part suggests that there is another set of data to which the observed set can be matched. This standard is the set of expected frequencies that are calculated in the course of computing the χ2 value. If the observed data fit, the χ2 value is just too close to what you would expect by chance and does not differ significantly. If the observed data do not fit, then what you observed is different
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