Different terminologies that help the interpretation of outcomes

Abstract

For the first of these, where the comparison is ‘before’ and ‘after’ for the same person, the noun ‘change’ is used (minimal important change, MIC). For the second, where the comparison is between a person’s outcome and a different person’s experience, ‘difference’ is used (minimal important difference, MID), for example when two people have undergone different types of surgery for the same disorder (fasciectomy versus collagenase would be an example). The schematic in Figure 1 shows how these terms apply to comparing operation A to operation B to operation C. All three groups of patients have the same average preoperative hand function score (the red, green and purple circles, respectively). Both operation A and operation B work, hence both of these groups have a hand-function score improvement following treatment. For both operations A and B, the improvement in score exceeds the MIC. Thus, both treatments were considered worthwhile by the patients and delivered real-world improvement. In contrast, the improvement from operation C is smaller than the MIC, and so this treatment does not deliver meaningful change, even if the preto postoperative change turns out to be statistically significant (as might occur if the group was large). Taking this further, the two effective treatments work differently: operation B achieves a greater hand function improvement than operation A, and the difference between the groups is larger than the MID. Thus, the patients who received operation A might say ‘I did get better from operation A – it was worthwhile . . . but I would have been noticeably happier if I’d had operation B’.