Psychometric performance of the Primary Mitochondrial Myopathy Symptom Assessment (PMMSA) in a randomized, double-blind, placebo-controlled crossover study in subjects with mitochondrial disease

Journal of Patient-Reported Outcomes

Table 9 Candidate clinically important differences for 4FS and individual PMMSA items

Measure	Distribution-based methods		Anchor-based methods
Measure	½ SD	SEM	PGA	PhGA	6MWT	Median
4FS weekly score	1.25	0.79	2.14	1.53	2.05	2.05
Tiredness at rest	0.33	0.29	0.46	0.31	0.55	0.46
Tiredness during activities	0.32	0.25	0.56	0.4	0.62	0.56
Muscle weakness at rest	0.36	0.22	0.47	0.36	0.39	0.39
Muscle weakness during activities	0.36	0.2	0.65	0.47	0.49	0.49
Balance problems	0.39	0.22	0.27	0.03	0.35	0.27
Vision problems	0.51	0.2	0.23	0.04	0.24	0.23
Abdominal discomfort	0.29	0.21	0.29	0.07	0.26	0.26
Muscle pain	0.47	0.21	0.55	0.22	0.38	0.38
Numbness	0.43	0.31	–	0.04	0.07	0.06
Headache	0.43	0.18	0.34	0.07	0.61	0.34

–indicates a logically inconsistent value was found, in which improved patients had worse PMMSA item scores, and this value was excluded as a candidate threshold value
4FS = Fatigue 4 Scale; 6MWT = six-minute walk test; PGA = Patient Global Assessment; PhGA = Physician Global Assessment; SD = standard deviation; SEM = standard error of measurement