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The challenge is to separate fully the effect of the year of inclusion in the register and the effect of duration of the disease
A pivotal question when evaluating the long term outcome of patients with rheumatoid arthritis (RA) is how the disease itself evolves over time and to what extent new treatments contribute to such changes. Insight into the evolution of the manifestations of RA can help to define agendas for research and healthcare delivery world wide. In this issue of the Annals Heiberg et al describe “7 year changes in health status and priorities for improvement of health in patients with rheumatoid arthritis” and conclude that “although pain remained the area of highest priority for improvement among patients, the health status improved from 1994 to 2001, probably owing to access to better and more aggressive treatments”.1 In this editorial, we will briefly elaborate on the strengths of longitudinal observational studies (LOS), in general, and on the relative importance of research on patient priorities in such studies, in particular. Next, we will discuss the subject of time and change over time in longitudinal studies in the light of the conclusion drawn from the present study.
Longitudinal observational studies and patient perspective as an outcome
The conclusion of the authors is based on an analysis of data from the Oslo RA Register (ORAR), a continuing LOS that was started in 1994 as a prevalent population based register, and annually updated with new cases since then.2 Longitudinal studies are particularly helpful in answering questions on causation, prognosis, and long term outcomes in the “real world” of healthcare delivery. In comparison with randomised clinical trials (RCTs), LOS are characterised by a higher level of external validity (because patients are not selected for high disease activity or unfavourable prognosis, etc), an emphasis on long term evaluation, and a view on …