A researcher studies systolic blood pressure (SBP) in 200 hypertensive patients. The mean SBP is 158 mmHg with a standard deviation of 20 mmHg. If SBP is normally distributed, the percentage of patients expected to have SBP between 138 and 178 mmHg is:
- A 50%
- B 68% ✓
- C 95%
- D 99.7%
Correct answer: B. 68%
Explanation
In a normal distribution, mean ± 1 SD covers approximately 68% of observations. Here, 138 = 158 − 20 and 178 = 158 + 20, which represents mean ± 1 SD. Mean ± 2 SD covers 95% and mean ± 3 SD covers 99.7%. The range 138−178 corresponds to exactly one standard deviation on each side of the mean.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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