A study reports a 95% confidence interval for the difference in mean hemoglobin between two groups as (-0.5 to 3.5 g/dL). Which statement is correct?
- A The difference is statistically significant at p < 0.05
- B The p-value is exactly 0.05
- C The null hypothesis of no difference cannot be rejected at alpha = 0.05 ✓
- D The study has proven that the two groups have equal hemoglobin
Correct answer: C. The null hypothesis of no difference cannot be rejected at alpha = 0.05
Explanation
A 95% confidence interval that includes zero means the null hypothesis of no difference cannot be rejected at the 0.05 level. Option A is the opposite of the correct interpretation. Option B cannot be determined exactly from the interval alone. Option D is wrong because failure to reject the null does not prove equality; it only indicates insufficient evidence of a difference.
Reference: Ganong's Review of Medical Physiology, 26th ed.
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