A sample of 400 adults shows a mean systolic BP of 128 mmHg with SD of 20 mmHg. The 95% confidence interval for the population mean is approximately:

• A 88–168 mmHg
• B 118–138 mmHg
• C 124–132 mmHg
• D 126–130 mmHg ✓

Explanation

Standard Error (SE) = SD/√n = 20/√400 = 20/20 = 1 mmHg. 95% CI = mean ± 1.96 × SE = 128 ± 1.96 ≈ 126–130 mmHg. A larger sample produces a narrower CI, reflecting greater precision. The CI means that 95% of similarly constructed intervals from repeated sampling would contain the true population mean; it does not mean a 95% probability that the parameter lies within this specific interval.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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