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Expanding the definition of clinical differences: from minimally clinically important differences to really important
Frederick Wolfe1, Kaleb Michaud, Vibeke Strand
1Arthritis Research Center Foundation and the University of Kansas School of Medicine, Wichita, Kansas 67214, USA. fwolfe@arthritis-research.org
Objective:
Minimally clinically important differences (MCID) have become an important way to interpret data of randomized clinical trials (RCT), but do not reflect the degree of improvement consistent with a "really important difference" (RID). To define RID, we compared mean and/or least desirable clinical states with best and/or most desirable states.
Methods:
In total, 8931 patients with rheumatoid arthritis (RA) < 65 years of age completed the Health Assessment Questionnaire (HAQ) and Medical Outcomes Survey Short Form 36 Physical Component Score (PCS). Definitions of RID were based on values for HAQ and PCS corresponding with the best and worst category of the following conditions: disabled vs not disabled: joint replacement vs no joint replacement; < poverty level vs > poverty level; very satisfied with health vs not; and independent in participation activities vs not.
Results:
In contrast to published MCID values for the HAQ of approximately 0.22, RID was as high as 0.76 using objective reference conditions and 0.87 using the subjective measure of dependence vs independence. The HAQ score of independent RA patients was 0.38 (SD 0.45), and was 0.42 (SD 0.53) for those very satisfied with their health. The difference in HAQ scores between disabled and working patients was approximately 0.75. PCS differences were similarly increased.
Conclusion:
RID values are 3 to 4 times greater than MCID values. Although MCID are meaningful statistics for RCT, the RID percentage achieved [(actual improvement/RID) 100%] is a simple way to put the results of RCT in a broader perspective that gives an idea of how much additional treatment effect is needed.
Insights
Really Important Difference (RID) values are substantially larger than Minimally Clinically Important Differences (MCID), offering a better perspective on treatment effects in rheumatoid arthritis randomized clinical trials.
Area of Science:
- Rheumatology
- Clinical Trial Methodology
- Health Outcomes Research
Background:
- Minimally Clinically Important Differences (MCID) are commonly used to interpret randomized clinical trial (RCT) data.
- MCID may not fully capture the magnitude of improvement that constitutes a
- really important difference
- (RID).
Purpose of the Study:
- To define and establish Really Important Difference (RID) values.
- To compare RID with MCID for interpreting clinical trial outcomes in rheumatoid arthritis (RA).
Main Methods:
- Defined RID by comparing mean/least desirable clinical states with best/most desirable states in 8931 RA patients (<65 years).
- Utilized Health Assessment Questionnaire (HAQ) and SF-36 Physical Component Score (PCS) data.
- RID was based on objective (e.g., joint replacement) and subjective (e.g., health satisfaction) conditions.
Main Results:
- RID values for HAQ were significantly higher (0.76 objective, 0.87 subjective) than published MCID values (~0.22).
- HAQ scores for independent RA patients (0.38) and those very satisfied with health (0.42) informed RID.
- Differences in HAQ and PCS scores between distinct clinical states were substantially larger than MCID.
Conclusions:
- RID values are 3 to 4 times greater than MCID values.
- The percentage of RID achieved provides a valuable metric for contextualizing RCT results.
- This metric indicates the remaining treatment effect needed for a truly meaningful improvement.
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