Potential impact of observational cohort studies in Japan on rheumatoid arthritis research and practice.

For better management of rheumatoid arthritis (RA) patients, we need information both from well-designed clinical trials, such as randomized controlled trials, and from observational cohorts. Observational cohort study has not been developed in Japanese RA patients; however, two cohorts, IORRA (formerly J-ARAMIS) from 2000 and NinJa by iR-net from 2002, have been established. These two cohorts are an important source not only for better management of Japanese RA patients but also for solutions to a variety of issues concerning RA clinical practice in general. In this minireview, necessities of observational cohort studies are discussed.