## **Core Concept**
The killing power of a disease is an important epidemiological measure that reflects the severity or deadliness of a condition. It is quantitatively expressed using specific terms that denote the proportion of individuals who die from a particular disease. **Mortality rate** is a key concept here, which is a measure of the number of deaths (in a given population) due to a specific disease over a certain period.

## **Why the Correct Answer is Right**
The correct answer, **Case Fatality Rate ( CFR)**, is a measure of the severity of a disease and is defined as the proportion of deaths within a designated population of people with a particular condition over a certain period of time. It is calculated as the number of deaths due to a specified disease divided by the number of individuals diagnosed with the disease, usually expressed as a percentage. CFR directly reflects the killing power or lethality of a disease.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While this option is not provided, typically, **Incidence Rate** refers to the number of new cases that develop in a specified time period among a population at risk, which does not directly denote killing power.
- **Option B:** Similarly, **Prevalence Rate** measures the total number of cases of a disease in a population at a given time, which includes both new and existing cases. This does not directly indicate the lethality of a disease.
- **Option D:** **Attack Rate** is a measure used in epidemiology to express the frequency of occurrence of a disease or condition in a population at risk over a specified period. It does not specifically denote the killing power of a disease.

## **Clinical Pearl / High-Yield Fact**
A critical point to remember is that **Case Fatality Rate (CFR)** varies significantly among diseases and can be influenced by factors like healthcare quality, age of the population, and the presence of comorbid conditions. For example, diseases with high CFR include rabies, Ebola, and untreated HIV infection in certain populations.

## **Correct Answer:** . Case Fatality Rate.