Incidence
Also called: TB incidence, Disease incidence rate · Topic: Economic Data: Census, NSS, Surveys and Statistical Tools · NCERT: Beyond NCERT
Meaning
Incidence is the number of new cases of a disease that appear in a population during a given period, usually one year. It is normally given as a rate per 1,00,000 people, so that places with different population sizes can be compared:
Incidence rate = (new cases in the year ÷ population) × 1,00,000
Incidence shows how fast a disease is spreading. It falls only when fewer people catch the disease, so it is the best test of whether transmission (the disease passing from person to person) is being stopped.
Example
India's TB incidence fell from 237 per lakh in 2015 to 187 per lakh in 2024 (WHO Global TB Report 2025). That is a fall of about 21%. Over a similar period, TB deaths fell 38%. Better treatment saved more patients, but new infections fell much more slowly.
Don't confuse with
- Prevalence: the total number of people who have the disease at a point in time, both old and new cases. Incidence counts only the new cases.
- Notifications / mortality: notifications are the cases reported to the government, and they rise when screening gets better even if the disease is falling. Mortality counts deaths, and it can fall through better treatment alone, without any fall in incidence.