Question:
Prevalence of a disease:
Prevalence of a disease:
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Prevalence = incidence x average duration; duration is shortened by death or cure, so prevalence reflects that balance.
Updated On: Jul 8, 2026
- Is the best measure of disease frequency in etiological studies.
- Can only be determined by a cohort study.
- Is the number of new cases in a defined population.
- Describes the balance between incidence, mortality and recovery.
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Question.
We need to pick the statement that correctly describes prevalence, one of the two basic measures of disease frequency along with incidence.
Step 2: Key Formula or Approach.
Prevalence is the total number of existing cases (old plus new) of a disease in a population at a given point or period of time. It is linked to incidence and average duration of disease by the simple relation
\[ \text{Prevalence} \approx \text{Incidence} \times \text{Average duration of disease} \]
The duration of disease, in turn, is shortened by death or recovery/cure. So the size of the prevalence pool at any time reflects the balance between how fast new cases flow in (incidence) and how fast old cases flow out (through death, recovery, or migration).
Step 3: Detailed Explanation.
Option (A) is wrong because incidence, not prevalence, is the preferred measure in etiological (cause-finding) studies, since incidence reflects new disease events and risk over time; prevalence mixes new and old cases and is affected by survival, so it is a poor tool for studying causation.
Option (B) is wrong because prevalence is usually found through a cross-sectional (survey type) study done at one point in time, not only through a cohort study.
Option (C) is wrong because "number of new cases" is the definition of incidence, not prevalence; prevalence counts all existing cases, old and new, at that time.
Option (D) is correct: prevalence rises when incidence rises or when patients live longer with the disease (less death, slower cure), and it falls when incidence drops or cases are removed quickly by death or recovery. So prevalence reflects this ongoing balance between incidence, mortality, and recovery.
Step 4: Final Answer.
Prevalence describes the balance between incidence, mortality, and recovery.
\[ \boxed{\text{Describes the balance between incidence, mortality and recovery}} \]
We need to pick the statement that correctly describes prevalence, one of the two basic measures of disease frequency along with incidence.
Step 2: Key Formula or Approach.
Prevalence is the total number of existing cases (old plus new) of a disease in a population at a given point or period of time. It is linked to incidence and average duration of disease by the simple relation
\[ \text{Prevalence} \approx \text{Incidence} \times \text{Average duration of disease} \]
The duration of disease, in turn, is shortened by death or recovery/cure. So the size of the prevalence pool at any time reflects the balance between how fast new cases flow in (incidence) and how fast old cases flow out (through death, recovery, or migration).
Step 3: Detailed Explanation.
Option (A) is wrong because incidence, not prevalence, is the preferred measure in etiological (cause-finding) studies, since incidence reflects new disease events and risk over time; prevalence mixes new and old cases and is affected by survival, so it is a poor tool for studying causation.
Option (B) is wrong because prevalence is usually found through a cross-sectional (survey type) study done at one point in time, not only through a cohort study.
Option (C) is wrong because "number of new cases" is the definition of incidence, not prevalence; prevalence counts all existing cases, old and new, at that time.
Option (D) is correct: prevalence rises when incidence rises or when patients live longer with the disease (less death, slower cure), and it falls when incidence drops or cases are removed quickly by death or recovery. So prevalence reflects this ongoing balance between incidence, mortality, and recovery.
Step 4: Final Answer.
Prevalence describes the balance between incidence, mortality, and recovery.
\[ \boxed{\text{Describes the balance between incidence, mortality and recovery}} \]
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