A study assessing association between categorical variables (smoking: yes/no) and disease outcome (lung cancer: yes/no) in a 2×2 table should use which statistical test when all expected cell frequencies are ≥ 5?
- A Chi-square test of independence ✓
- B Fisher's exact test
- C Student's t-test
- D One-way ANOVA
Correct answer: A. Chi-square test of independence
Explanation
Chi-square (χ²) test of independence is the appropriate test for assessing association between two categorical variables in a 2×2 contingency table when all expected cell frequencies are ≥ 5. When expected frequencies are < 5 in any cell, Fisher's exact test is preferred (especially when total n < 20). Student's t-test compares means of continuous variables between two independent groups. ANOVA compares means across three or more groups. The χ² test gives p-value but not the direction or magnitude of association — OR or RR is needed for that.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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