A study of 1000 individuals finds systolic blood pressure data with mean = 120 mmHg and standard deviation = 10 mmHg. Assuming normal distribution, the number of individuals expected to have SBP between 110 and 130 mmHg is approximately:
- A 760
- B 680 ✓
- C 950
- D 997
Correct answer: B. 680
Explanation
In a normal distribution, 68.27% of values fall within ±1 SD of the mean (mean ± 1 SD = 110–130 mmHg). In 1000 individuals, approximately 683 ≈ 680 individuals are expected within this range. The range ±2 SD covers 95.45% and ±3 SD covers 99.73%.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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