VALIDATION DATA

The validation strategy included 130 patients from September 2016 to September 2018. Out of 130 participants, 108 (83%) were women. The mean age was 56.4±2.1 years. Around 31.5% (39/124) of participants were living alone, while 48.8% (60/123) had secondary education. About 27.8% (35/126) had higher socio-professional status. The median disease duration was 9 years (interquartile range: 4 to 23 years).

Internal validity (Kuder–Richardson alpha) coefficient was 0.90. The correlation between items and total long-form RAKE score (“item-retest correlation”) varied between 0.01 and 0.57.

Reproducibility was good (ICC= 0.86 [0.80; 0.92])

The questionnaire was developed in three steps. Firstly, 90 knowledge items were extracted from published and unpublished questionnaires, which were then used in a Delphi process involving rheumatologists, health professionals, and patients to identify relevant knowledge for RA patients. The Delphi rounds involved 107 participants from 13 teams across France, resulting in a list of 322 items. In the second step, a final Delphi round selected a list of 45 essential and useful items for the study, and a questionnaire was constructed with each question referring to a selected item. The questionnaire was then reformulated, validated linguistically and cognitively, and reviewed by investigating centers to obtain the final version.

Number of missing data per item was <5% and total rate of missing data was 1.2% indicating good acceptability.

RAKE score was correlated with the degree of information the patient had about his or her disease and treatment according to the doctor or the nurse (respectively r = 0.55, r= 0.58)(positive correlation), and  with the patients’ level of education (p < 0.001) (positive correlation).