Calculate the prevalence if incidence is 2 cases per 1000 population per year and mean duration is 4 years-
**Core Concept**
The prevalence of a disease is the total number of cases present in a population at a given time, while the incidence is the number of new cases that develop in a population over a specified period. Prevalence can be calculated using the formula: Prevalence = Incidence x Mean Duration.
**Why the Correct Answer is Right**
To calculate the prevalence, we need to multiply the incidence rate by the mean duration of the disease. Given an incidence rate of 2 cases per 1000 population per year and a mean duration of 4 years, we can calculate the prevalence as follows: Prevalence = 2 cases/1000/year x 4 years = 8 cases/1000 population.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option would be incorrect if it provided a different calculation method or a different value for mean duration.
* **Option B:** This option would be incorrect if it failed to account for the mean duration or provided an incorrect value for incidence.
* **Option C:** This option would be incorrect if it provided a value that is not a result of the calculation (e.g., a percentage instead of a ratio).
* **Option D:** This option would be incorrect if it failed to provide a clear calculation or formula.
**Clinical Pearl / High-Yield Fact**
Remember that prevalence is a function of both incidence and mean duration, and it provides a snapshot of the total disease burden in a population at a given time.
**Correct Answer: A. 8 cases/1000 population.**