Incidence is defined as –
**Core Concept**
Incidence refers to the number of new cases of a disease or condition that occur within a specified time period among a population at risk. It is a measure of the rate of occurrence of new events, and it helps in understanding the burden of disease and the effectiveness of interventions.
**Why the Correct Answer is Right**
Incidence is a fundamental concept in epidemiology, and it is calculated by dividing the number of new cases by the population at risk over a specified time period. This measure is essential in assessing the impact of a disease and evaluating the effectiveness of prevention and control strategies. Incidence is often expressed as a rate per 1,000 or 100,000 population per year.
**Why Each Wrong Option is Incorrect**
**Option A:** Prevalence is the total number of cases of a disease or condition in a population at a specific point in time, including both new and existing cases. It does not account for the occurrence of new cases.
**Option B:** Mortality rate refers to the number of deaths from a specific disease or condition within a population over a specified time period, expressed as a rate per 1,000 or 100,000 population per year. It does not measure the occurrence of new cases.
**Option C:** Morbidity rate refers to the number of cases of a disease or condition within a population over a specified time period, expressed as a rate per 1,000 or 100,000 population per year. While it measures the occurrence of disease, it includes both new and existing cases.
**Clinical Pearl / High-Yield Fact**
To remember the difference between incidence and prevalence, think of incidence as the "new cases" and prevalence as the "total cases".
**Correct Answer:** B.