Morbidity (illness) statistics are widely used by epidemiologists in the analysis of ill-health within human populations. There are two major types of morbidity rate: the prevalence rate and the incidence rate. The prevalence rate gives an indication of the number of individuals in a population suffering from a particular condition at any time, while the incidence rate shows how many individuals develop a condition within a particular period of time, usually one year. Morbidity rates are generally presented for specific conditions rather than as a general rate, and may be reported as absolute numbers within a year (for example 200 cases of rabies), or as incidence rates per thousand population, to facilitate comparisons between different sub-populations (such as sexes, age-groups, or occupations). Unlike mortality rates
, which are uniquely reported in official statistics
, morbidity statistics are available from a variety of sources, including the following: official statistics on contagious diseases and other notifiable illnesses, hospital in-patient records, records of claims for sickness benefit, and local or national interview surveys which obtain self-report data on ill-health.