The rate at which a disease occurs. IE; one in five people, one in twenty people, etc.
Gastrointestinal diseases (including gastric ulcers) affect an estimated 25-30% of the world's population.
The incidence will equal the prevalence when the duration of the disease is equal to the time period over which the incidence is measured.
The peak incidence is approximately age 62, but young-onset PD can occur as early as age 40.
onset /prevalence/
The incidence of disease is how frequent or widespread a disease is in the population. Severity is how bad and serious any particular disease is in a person.