Content validity of the Dutch Rheumatoid Arthritis Impact of Disease (RAID) score: results of focus group discussions in established rheumatoid arthritis patients and comparison with the International Classification of Functioning, Disability and Health core set for rheumatoid arthritis

BACKGROUND The Rheumatoid Arthritis Impact of Disease (RAID) score was developed as a European League Against Rheumatism initiative to obtain a patient reported outcome score for clinical trials in patients with rheumatoid arthritis (RA), based on patients' perception of the impact of the disease on several domains of health. The objective of this study was to assess the content validity of this score in Dutch RA patients. METHODS During three focus group discussions (n = 23), patients with RA reflected on comprehensiveness of the RAID to measure impact of RA on their life, relevance of the RAID domains and formulation of questions. Also, the domains of the RAID score were compared to the comprehensive International Classification of Functioning, Disability and Health core set for RA. RESULTS Patients confirmed that RA had impact on five domains already incorporated in the RAID score: emotional well-being, pain, performing daily activities, fatigue and coping. There was variation in interpretation of some of the items of the RAID score, suggesting problems in comprehension. Patients indicated that the domains work, relationships with others (such as family and friends) and spare time/hobbies were missed in the RAID and could be added to obtain a more 'complete' picture of the impact of the disease. CONCLUSION The RAID score has fairly good content validity. If confirmed as important in other patient groups, items in the above mentioned areas should be considered in a future upgrade.