In a study comparing mean blood pressure between two independent groups, an independent samples t-test gives p = 0.03. The 95% confidence interval for the mean difference is 2 to 18 mmHg. The correct interpretation is:
- A The true mean difference lies between 2 and 18 mmHg with 95% confidence; the result is statistically significant ✓
- B There is a 95% probability that the next patient's difference will be between 2 and 18 mmHg
- C 95% of sample mean differences from repeated studies will lie between 2 and 18 mmHg
- D The study has 95% power to detect a true mean difference of 10 mmHg
Correct answer: A. The true mean difference lies between 2 and 18 mmHg with 95% confidence; the result is statistically significant
Explanation
A 95% confidence interval for the mean difference means that if the study were repeated many times with the same methods, 95% of the resulting CIs would contain the true population mean difference. In this instance, we are 95% confident the true mean difference falls between 2 and 18 mmHg. The CI does not cross zero and p < 0.05, confirming statistical significance. Option B describes a prediction interval for an individual, not a CI. Option C incorrectly describes the sampling distribution. Option D defines statistical power, which is separate from the CI.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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