The drive towards an established of a core set of outcomes for RA has been mainly due to the development of the international initiative known as the Outcome Measures in Rheumatology (OMERACT) group. OMERACT is the acronym for an international, informally organized network initiated in 1992 aimed at improving outcome measurement in rheumatology. OMERACT was established to review and recommend a core set of outcomes which would appropriately measure the impact of treatment on chronic musculoskeletal diseases. While the remit of the group was originally clinical trials in relation to RA, it now encompasses a broad range of diseases within the musculoskeletal disease group. Data driven recommendations are prepared and updated by expert working groups and recommendations include core sets of measures for most of the major rheumatologic conditions (Tugwell and Boers 1993). OMERACT have succeeded in achieving consensus on core sets of measures for RA, osteoarthritis and osteoporosis, psoriasis/ psoriatic arthritis, on psychosocial measures and core set of data for cost-effectiveness evaluations. The review process must satisfy the OMERACT fi lter which encompasses three fi lters; truth (does it measure what it is supposed to), discrimination (can the measure discriminate between situations of interest) and feasibility (is it understandable and cheap).