Question

What happens to the prevalence of a disease if the duration of the illness increases while incidence remains constant?

• A. Decreases
• B. Remains unchanged
• C. Increases
• D. Becomes zero

Hint:

Prevalence $\propto$ Duration. Longer disease duration $\Rightarrow$ More existing cases.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Incidence measures new cases, while prevalence measures all existing cases.
Step 2: Key Formula or Approach:
The relationship between prevalence (\(P\)), incidence (\(I\)), and average duration (\(D\)) is expressed as:
\[ P \approx I \times D \]
Step 2: Detailed Explanation:
If the incidence (\(I\)) is constant, but the duration (\(D\)) of the illness increases (e.g., people live longer with a chronic disease due to better care), the number of people living with the disease at any given time will go up.
Mathematically, if \(D\) increases in the formula \(P \approx I \times D\), then \(P\) must also increase.
Step 3: Final Answer:
The prevalence of the disease increases.