A survey of 200 pregnant women finds that 50 are anaemic. The standard error of this proportion is approximately:
- A 0.031 ✓
- B 0.025
- C 0.018
- D 0.044
Correct answer: A. 0.031
Explanation
The proportion p = 50/200 = 0.25. Standard error of proportion = sqrt[p(1-p)/n] = sqrt[0.25 x 0.75 / 200] = sqrt[0.1875/200] = sqrt[0.0009375] = 0.0306, approximately 0.031. This formula is standard for estimating precision of a proportion.
Reference: Park's Textbook of Preventive and Social Medicine, 26th ed.
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