Incidence is the number of new cases of a condition, symptom, death, or injury that develop during a specific time period, such as a year. The number is often expressed as a percentage of a population. For example, 25% of Americans were diagnosed with the flu in 2002.
Incidence shows the likelihood that a person in that population will be affected by the condition.
Reviewed By: Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.