2–5% of the AP exam. Key topics: Chi-square goodness-of-fit test: one sample, one categorical variable vs. a claimed distribution, Chi-square test for homogeneity: multiple populations, one categorical variable, Chi-square test for independence: one population, two categorical variables, Expected counts formula: (row total × column total) / table total, Conditions for chi-square inference: Random, 10%, all expected counts ≥ 5, Degrees of freedom: df = k − 1 (GOF); df = (r−1)(c−1) (homogeneity/independence), Chi-square statistic: χ² = Σ((O − E)² / E), Interpreting chi-square test results in context.
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