The population based studies in rheumatoid arthritis. A method of longterm followup studies

This article describes the aim, organization, data collection, and selected results from the Oslo Rheumatoid Arthritis Register (ORAR). The ORAR was established in 1994 and is annually updated with new and diseased cases. Inclusion criteria were a diagnosis of rheumatoid arthritis (RA) and a residential address in Oslo. As of January 1, 1994, Oslo had 477,781 inhabitants, 2 centers providing rheumatological health services, in close collaboration with general practitioners, and no fulltime private practising rheumatologists. Patients with RA ever treated in one of the 2 hospitals were identified and enrolled in ORAR. We assumed that patients in ORAR represented the majority of patients with RA in the county. Data collections have been performed as mail surveys and clinical examinations. By January 1, 1994, 1552 RA patients were included in the register; currently, 1626 are included. The completeness of the register has been estimated to be about 85%, based on a population survey. Response rates in ORAR surveys and clinical examinations have been between 60% and 80%. Results have been provided, for example, on incidence and prevalence linked to health outcomes, performance of health status measures, and occurrence of osteoporosis and secondary Sjögren's syndrome. The ORAR has provided epidemiological data that is representative of the entire patient population in the county.