To evaluate the agreement between the Routine Assessment of Patient Index Data 3 (RAPID-3) and a modified version of the Rheumatoid Arthritis Disease Activity Index (RADAI-5), as well as the Disease Activity Score including a 28 joint count (DAS28-ESR) and the Clinical Disease Activity Index (CDAI) in daily routine.
One hundred and twenty-eight rheumatoid arthritis (RA) out-patients completed the RADAI-5 and the RAPID-3. Simultaneously, the DAS28-ESR and the CDAI were applied. Cronbach's Alpha as a measure for reliability was calculated and factorial analysis was performed. For agreement analysis, Kendall's Tau was calculated.
Time to score the questionnaires was 25seconds. The median RADAI-5 was 2.8 (0-9.2), the median RAPID-3 3.3 (0-8.6), the median DAS28-ESR 2.95 (0.43-6.24), and the median CDAI 5.6 (0-37.5). Cronbach's Alpha for the RADAI-5 was 0.906 and 0.871 for the RAPID-3, however, only 0.165 for the DAS28-ESR and 0.210 for the CDAI, respectively. Factorial analysis revealed that both questionnaires and the DAS28-ESR, but not the CDAI, constitute mono-dimensional instruments. Tau for the agreement between the RADAI-5 and the RAPID-3 appeared to be 0.587 (p<0.001), and to be 0.582 (p<0.001) between the DAS28-ESR and the CDAI, while it was lower for the relationship between the questionnaires and the composite indexes.
Reliability of the RAPID-3 and RADAI-5 was significantly higher than of the indexes. The questionnaires as well as the indexes proved to be in highly moderate agreement, while agreement between the questionnaires and the indexes appeared to be lower.