Incidence is a contrasting term to prevalence. Incidence tells us the frequency of occurrence of some event during a particular time period. For example there were 581 criminal homicides in 1997, or the rate of crime for one year is higher than for the previous year. Incidence is the number of new cases of a condition, symptom, death, or injury that arise during a specific period of time, such as in a year. It 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.
Incidence proportion, known as cumulative incidence, is the number of new cases within a specified time period divided by the size of the population initially at risk. The incidence rate is the number of new cases per unit of person-time at risk.
Cumulative incidence is the incidence calculated using a period of time during which all of the individuals in the population are considered to be at risk for the outcome. It is sometimes referred to as the incidence proportion.
The term prevalence, in epidemiology, tells us about the number of particular events in the community. AIDS for example may be very prevalent (the total number with this syndrome) but the incidence (new cases) is going down each year.
Examples of incidence studies:
Differentials in the incidence of births while on
welfare: Evidence from Maryland
Ahmed, Ashraf U., Hill, Robert B.
Abstract: The welfare debate in Maryland centers on births while on public assistance. Differentials in the incidence of births while on welfare were studied using Quality Control data for the 1991-1992 period. The results show that around one-quarter of recipient children were born on welfare and that there were higher rates of such births amongst young mothers with less than high-school education, who had never married, and were Baltimore residents.
Changes in the Incidence and Duration of Periods without Insurance
David M. Cutler, Ph.D., and Alexander M. Gelber, Ph.D.
ABSTRACT: Background Policymakers have recently proposed ways of providing health care coverage for an increased number of uninsured persons. However, there are few data that show how the incidence and duration of periods in which persons do not have insurance have changed over time.
Diabetes Incidence Based on Linkages With Health Plans: The Multiethnic Cohort
Gertraud Maskarinec, Eva Erber, Andrew Grandinetti, Martijn Verheus, Robert Oum, Beth N. Hopping, Mark M. Schmidt, Aileen Uchida, Deborah Taira Juarez, Krista Hodges and Laurence N. Kolonel
Abstract: OBJECTIVE Using the Hawaii component of the Multiethnic Cohort (MEC), we estimated diabetes incidence among Caucasians, Japanese Americans, and Native Hawaiians.
Participation in Operation Starting Line,
Experience of Negative Emotions, and Incidence of Negative Behavior - Kent R.
Kerley, Todd L. Matthews, Jeffrey T. Schulz, Department of Sociology, Mississippi State
University, P.O. Box C, Mississippi State, Mississippi 39762, USA = International Journal
of Offender Therapy and Comparative Criminology, Vol. 49, No. 4, 410-426 (2005)
The prison industry in the United States has experienced an unprecedented period of growth during the past three decades. Growing dissatisfaction with the monetary investment in the criminal justice system, state-level budget constraints, and high recidivism rates have led many criminal justice professionals to rethink issues of offender resocialization and rehabilitation.