A researcher wants to compare the mean hemoglobin levels between two large groups (n=200 each). The population standard deviation is known from previous national surveys. The most appropriate test is:
- A Student's t-test
- B Z-test ✓
- C Mann-Whitney U test
- D Paired t-test
Correct answer: B. Z-test
Explanation
A Z-test is appropriate when the population standard deviation is known and sample size is large. Student's t-test is used when population SD is unknown and must be estimated from the sample. With large samples, t approximates z, but when population SD is genuinely known, z-test is theoretically correct. Mann-Whitney is for non-normal data. Paired t-test requires paired observations.
Reference: B K Mahajan's Methods in Biostatistics, 7th ed.
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