Responsiveness, minimal important difference, minimal relevant difference, and optimal number of patients for a study

Abstract

Several terms are used to describe changes in PROM scores in relation to treatments.Whether the change is small, large, or relevant is defined in different ways, yet these change scores are used to recommend or oppose treatments. They are also used to calculate the necessary number of patients for a study. This article offers a theoretical explanation behind the terms responsiveness, minimal important difference (MID), minimal important change (MIC), minimal relevant difference (MIREDIF), and threshold of clinical importance. It also gives instructions on how these and the optimal number of patients for a study are calculated. Responses to two domains of the Knee Injury and Osteoarthritis Outcome Score (KOOS), before and 1 year after reconstruction of the anterior cruciate ligament of 164 patients, are used to illustrate the calculations. This paper presents the most common methods used to calculate and interpret MID. Results vary substantially across domains, patient location on the scale, and health conditions. The optimal number of patients depends on the minimal relevant difference (MIREDIF), the standard error of the measure (SEM), the desired statistical power for the measurement, and the responsiveness of the measurement instrument (the PROM). There is often uncertainty surrounding the calculation and interpretation of responsiveness, MID, and MIREDIF, as these concepts are complex.When MID is used to evaluate research results, authors should specify how the MID was calculated, and its relevance for the study population. These measures should only be used after thorough consideration to justify healthcare decisions.

Potential problems in the use of patient reported outcome measures (PROMs) and reporting of PROM data in sports science

“…Also, there is often substantial variation in standard error of measurement, depending on where an individual's score is located on the scale, 22 which lowers the precision of the individual score.…”

Inter-Day Test–Retest Reproducibility of the CAT, CCQ, HADS and EQ-5D-3L in Patients with Severe and Very Severe COPD

“… 35 , 36 The MIC can be calculated in different ways and there is often uncertainty surrounding the calculation and interpretation of MIC. 50 In addition the MIC estimate may differ on the patients initial health status or symptom burden and the specific intervention delivered. 50 We found that the SRD for the CAT is lower than the previously reported MIC based on rehabilitations studies, 35 , 36 and this suggests that the MIC can be distinguished from repeated measurement error on a group level.…”

“… 50 In addition the MIC estimate may differ on the patients initial health status or symptom burden and the specific intervention delivered. 50 We found that the SRD for the CAT is lower than the previously reported MIC based on rehabilitations studies, 35 , 36 and this suggests that the MIC can be distinguished from repeated measurement error on a group level. Thus, it appears that CAT is acceptable for evaluative purposes in a group of patients with severe and very severe COPD.…”

“… 31 , 49 MIC is often referred to as the minimal important difference (MID) or the minimal clinical important difference (MCID), and because that they constitute the same, they are used interchangeably in the literature. 50 …”

Choosing the most appropriate PROM for clinical studies in sports medicine

“…However, if one of the first two options is chosen, the author(s) should explain the rationale for this choice, and possible consequences for the validity and trustworthiness of the study need to be discussed. PROMs that lack robust measurement properties are less responsive to changes in the underlying clinical condition, 34 and using inadequate PROMs can lead to flawed conclusions and must be avoided.…”