How is case-fatality rate defined?

• A. The number of people who die from a disease divided by the total population
• B. Deaths from a disease within a period divided by the total number who have the disease
• C. Proportion of deaths due to all causes
• D. Time from diagnosis to death

Answer: (B)

Case-fatality rate tells you how deadly a disease is among the people who actually have it. It is defined as the number of deaths from the disease within a specified period divided by the total number of people known to have the disease during that same period. For example, if 100 people are diagnosed and 5 die during the follow-up period, the case-fatality rate is 5%. This measure reflects lethality conditional on being a case, not the risk of dying in the whole population.

This is different from the mortality rate, which would use deaths divided by the total population, regardless of who was diseased. It also isn’t the proportion of deaths from all causes, nor the time from diagnosis to death. CFR can be influenced by how completely cases are identified and how long you follow people after diagnosis, so it’s most accurate when there’s complete follow-up or a clearly defined period with outcomes known.