A 2x2 table from a rare disease outbreak contains several cells with expected frequencies below 5. Which test should be applied to assess association?
- A Pearson chi-square test without correction
- B Student t-test
- C Fisher's exact test ✓
- D McNemar's test
Correct answer: C. Fisher's exact test
Explanation
Chi-square approximation becomes unreliable when any expected cell frequency falls below 5, especially with small total numbers. Fisher's exact test calculates the exact probability of the observed table under the null hypothesis and is valid regardless of expected counts. Yates correction is used when only some expected values are marginally below 5, and McNemar applies to paired categorical data, neither of which fits this situation.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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