A statistical significance test based on frequency of occurrence; it is applicable both to qualitative attributes and quantitative variables. Among its many uses, the most common are tests of hypothesized probabilities or probability distributions (goodness of fit), statistical dependence or independence (association), and common population (homogeneity). The formula for chi square (χ2) depends upon intended use, but is often expressible as a sum of terms of the type (f − h)2/h where f is an observed frequency and h its hypothetical value.