Defining cut-off values for disease activity states and improvement scores for patient-reported outcomes: The example of the Rheumatoid Arthritis Impact of Disease (RAID)

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Abstract

Introduction: The Rheumatoid Arthritis Impact of Disease (RAID) is a patient-reported outcome measure evaluating the impact of rheumatoid arthritis (RA) on patient quality of life. It comprises 7 domains that are evaluated as continuous variables from 0 (best) to 10 (worst). The objective was to define and identify cut-off values for disease activity states as well as improvement scores in order to present results at the individual level (for example, patient in acceptable state, improved patient).Methods: Patients with definite active RA requiring anti-tumour necrosis factor (anti-TNF) therapy were seen at screening, baseline and after 4 and 12 weeks of etanercept therapy. Answers to "Gold standard" questions on improvement (MCII: Minimum Clinically Important Improvement) and an acceptable status (PASS: Patient Acceptable Symptom State) were collected as well as the RAID score and Disease Activity Score 28- erythrocyte sedimentation rate (DAS28-ESR). Cut-offs were defined by different techniques including empirical, measurement error and gold standard anchors. The external validity of these cut-offs was evaluated using the positive likelihood ratio (LR) based on the patient's perspective (for example, patient's global) and on low disease activity status (such as DAS28-ESR).Results: Ninety-seven (97) of the 108 recruited patients (age: 54 ± 13 years old, female gender: 75%, rheumatoid factor positive: 81%, disease duration: 8 ± 7 years, CRP: 18 ± 30 mg/l, DAS28-ESR: 5.4 ± 0.8) completed the 12 weeks of the study. The different techniques suggested thresholds ranging from 0.2 to 3 (absolute change) and from 6 to 50% (relative change) for defining MCII and thresholds from less than 1 to less than 4.2 for defining PASS. The evaluation of external validity (LR+) showed the highest LR+ was obtained with thresholds of 3 for absolute change; 50% for relative change and less than 2 for an acceptable status.Conclusions: This study showed that thresholds defined for continuous variables are closely related to the methodological technique, justifying a systematic evaluation of their validity. Our results suggested that a change of at least 3 points (absolute) or 50% (relative) in the RAID score should be used to define a MCII and that a maximal value of 2 defines an acceptable status.Trial Registration: Clinicaltrial.gov: NCT004768053. © 2012 Dougados et al.; licensee BioMed Central Ltd.

Figures

  • Table 1 Rheumatoid Arthritis Impact of Disease questionnaire*
  • Figure 1 Reliability of the rheumatoid arthritis impact of disease (RAID) score shown by Bland & Altman graphic representation. *Mean of RAID score values between screening and baseline; **difference in RAID score between screening and baseline. The data lines represent the 95% confidence interval resulting in a smallest detectable change of 1.3 (for example, smallest detectable difference = 1.8).
  • Figure 2 Correct classification probability curve showing absolute change in rheumatoid arthritis impact of disease (RAID) score at week 4.
  • Table 2 Elaboration and evaluation of the external validity of the different potential thresholds defining a relevant improvement in the rheumatoid arthritis impact of disease (RAID) score
  • Figure 3 Receiver operating characteristic curve showing absolute change in rheumatoid arthritis impact of disease (RAID) score at week 4.
  • Figure 4 Distribution of the absolute changes in rheumatoid arthritis impact of disease (RAID) score from baseline to week 4 in patients considering their condition to be slightly or moderately improved. EULAR, European League Against Rheumatism.
  • Figure 5 Proposals and evaluation of different thresholds for defining a clinically meaningful improvement in an absolute change in the rheumatoid arthritis impact of disease (RAID) score. a. Proposals of threshold according to different techniques and different times of evaluation. b. Evaluation of external validity (versus DAS28-ESR) of different proposed thresholds. c. Evaluation of external validity (versus patient’s global assessment) of different proposed thresholds. *Thresholds, proposal based on the following techniques and time of evaluation: a, 75th percentile technique at week 4; b, empirical technique and correct classification at week 4; c, smallest detectable change and 75th percentile at week 12; d, ROC technique at week 4; e, empirical technique and correct classification at week 4; f, correct classification at week 12; g, ROC technique at week 12. +Positive likelihood ratio (higher values are indicative of better performing thresholds. See Methods for further explanation). DAS28-ESR, Disease Activity Score 28-erythrocyte sedimentation rate; ROC, receiver operating characteristic.
  • Figure 6 Proposals and evaluation of different thresholds for defining a clinically meaningful improvement in a relative change in the rheumatoid arthritis impact of disease (RAID) score. a. Proposals of threshold according to different techniques and different times of evaluation. b. Evaluation of external validity (versus DAS28-ESR) of different proposed thresholds. c. Evaluation of external validity (versus patient’s global assessment) of different proposed thresholds. *Thresholds, proposal based on the following technique and time of calculation: a, 75th percentile technique at week 4; b, ROC technique at week 4; c, empirical technique; d, correct classification at week 4 and 75th percentile at week 12; e, 75th percentile at week 12; f, ROC technique at week 12; g, correct classification at week 12; h, empirical technique. +Positive likelihood ratio (higher values are indicative of better performing thresholds. See Methods for further information). DAS28-ESR, Disease Activity Score 28-erythrocyte sedimentation rate; ROC, receiver operating characteristic.

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CITATION STYLE

APA

Dougados, M., Brault, Y., Logeart, I., van der Heijde, D., Gossec, L., & Kvien, T. (2012). Defining cut-off values for disease activity states and improvement scores for patient-reported outcomes: The example of the Rheumatoid Arthritis Impact of Disease (RAID). Arthritis Research and Therapy, 14(3). https://doi.org/10.1186/ar3859

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