Reliability of patient-reported outcomes in rheumatoid arthritis patients: an observational prospective study.
OBJECTIVE
Patient-reported outcomes (PROs) such as pain, patient global assessment (PGA) and fatigue are regularly assessed in RA patients. In the present study, we aimed to explore the reliability and smallest detectable differences (SDDs) of these PROs, and whether the time between assessments has an impact on reliability.


METHODS
Forty RA patients on stable treatment reported the three PROs daily over two subsequent months. We assessed the reliability of these measures by calculating intraclass correlation coefficients (ICCs) and the SDDs for 1-, 7-, 14- and 28-day test-retest intervals.


RESULTS
Overall, SDD and ICC were 25 mm and 0.67 for pain, 25 mm and 0.71 for PGA and 30 mm and 0.66 for fatigue, respectively. SDD was higher with longer time period between assessments, ranging from 19 mm (1-day intervals) to 30 mm (28-day intervals) for pain, 19 to 33 mm for PGA, and 26 to 34 mm for fatigue; correspondingly, ICC was smaller with longer intervals, and ranged between the 1- and the 28-day interval from 0.80 to 0.50 for pain, 0.83 to 0.57 for PGA and 0.76 to 0.58 for fatigue. The baseline simplified disease activity index did not have any influence on reliability. Lower baseline PRO scores led to smaller SDDs.


CONCLUSIONS
Reliability of pain, PGA and fatigue measurements is dependent on the tested time interval and the baseline levels. The relatively high SDDs, even for patients in the lowest tertiles of their PROs, indicate potential issues for assessment of the presence of remission.
Division of Rheumatology, Department of Internal Medicine 3, Medical University Vienna and.
Paul
P
Studenic
Division of Rheumatology, Department of Internal Medicine 3, Medical University Vienna and.
Tanja
T
Stamm
Division of Rheumatology, Department of Internal Medicine 3, Medical University Vienna and 2nd Department of Medicine, Hietzing Hospital, Vienna, Austria.
Josef S
JS
Smolen
Division of Rheumatology, Department of Internal Medicine 3, Medical University Vienna and daniel.aletaha@meduniwien.ac.at.
Daniel
D
Aletaha
D000328:Adult; D000368:Aged; D018501:Antirheumatic Agents / Q000627:therapeutic use*; D001172:Arthritis, Rheumatoid / Q000175:diagnosis / Q000188:drug therapy* / Q000523:psychology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D063868:Patient Outcome Assessment; D011446:Prospective Studies; D011594:Psychometrics / Q000379:methods; D011788:Quality of Life; D015203:Reproducibility of Results; D012720:Severity of Illness Index
D018501:Antirheumatic Agents
RA; disease activity; outcomes research; patient perspective; patient reported outcomes; psychometrics; reliability; test–retest