A chronic disease has an incidence of 2 per 1000 per year and an average duration of 5 years, in a stable population. What is its approximate prevalence?
Answer and explanation
Correct answer: D. 10 per 1000
- Step 1: For a stable condition prevalence is approximately incidence multiplied by mean duration.
- Step 2: 2 per 1000 per year multiplied by 5 years = 10 per 1000.
Answer
10 per 1000.
Why not the others: 5 per 1000: 5 per 1000 is the duration alone expressed as a rate. 25 per 1000: 25 per 1000 adds rather than multiplies. 2 per 1000: 2 per 1000 is the incidence alone.
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