Cross-cultural adaptation and validation of the Thai version of the Rheumatoid Arthritis Disease Activity Index (RADAI)

The objective of this study was to translate and evaluate the psychometric properties of the Thai version of the Rheumatoid Arthritis Disease Activity Index (RADAI) in patients with rheumatoid arthritis (RA). We translated and modified the original RADAI into the Thai version. A total of 116 Thai patients with RA were consecutively recruited. For test–retest reliability, 115 patients undertook RADAI questionnaires for 2 consecutive days. To test construct validity, the correlation of the single RADAI items and RADAI total scores with measures of disease activity and functional status was evaluated. Reliability was assessed using Cronbach’s alpha and intra-class correlation (ICC). The number of missing items and time-to-complete questionnaire were collected to estimate its feasibility. The RADAI significantly correlated with disease activity measured by the Clinical Disease Activity Index (CDAI) (r = 0.71), the Disease Activity Score 28 (DAS28) (r = 0.56), patient global assessment of disease activity (r = 0.71), and physician global assessment of disease activity (r = 0.66) and functional status measured by the Health Assessment Questionnaire (r = 0.52). The RADAI had a moderate internal consistency (Cronbach’s alpha = 0.69) and high test–retest reliability (ICC = 0.83). Ninety-one percentage completed questionnaires without missing an item. Mean time-to-complete questionnaire (±SD) was 4.82 (±1.86) min. The Thai RADAI questionnaire is valid, reliable, and easy to use for assessing disease activity in daily practice and epidemiologic research. Its psychometric properties were comparable to the original version.