In a 2x2 contingency table comparing treatment outcome (cured/not cured) between two drugs, one cell has an expected frequency of 3. The total sample size is 25. Which test is most appropriate?
- A Fisher's exact test ✓
- B Chi-square test
- C McNemar's test
- D Z-test for proportions
Correct answer: A. Fisher's exact test
Explanation
Fisher's exact test is used when expected frequencies in a contingency table are below 5, particularly in small samples. Chi-square test is invalid with low expected frequencies. McNemar's test is for paired or matched data. Z-test for proportions is for comparing two independent proportions but assumes adequate sample size.
Reference: Methods in Biostatistics, 7th ed.
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