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 3 Average polychoric correlations among PMMSA items

Item Content	Tiredness at rest	Tiredness during activities	Muscle weakness at rest	Muscle weakness during activities	Balance problems	Vision problems	Abdominal discomfort	Muscle pain	Numbness	Headache
Tiredness at rest	1.00
Tiredness during activities	0.83	1.00
Muscle weakness at rest	0.82	0.74	1.00
Muscle weakness during activities	0.74	0.81	0.85	1.00
Balance problems	0.48	0.53	0.56	0.59	1.00
Vision problems	0.08	0.13	0.13	0.19	0.32	1.00
Abdominal discomfort	0.37	0.31	0.29	0.28	0.23	0.26	1.00
Muscle pain	0.38	0.41	0.45	0.51	0.24	0.07	0.49	1.00
Numbness	0.29	0.34	0.34	0.43	0.46	0.29	0.28	0.59	1.00
Headache	0.31	0.20	0.21	0.26	0.04	0.22	0.52	0.41	0.07	1.00

Presented as average polychoric correlation coefficients among PMMSA item scores across all assessment days (i.e., the analysis ignores time of assessment and averages scores generated from daily responses for Day -6 [from screening], Day 1 [Baseline], and every subsequent 10th day [Days 11, 21, and up to Day 101])
PMMSA = Primary Mitochondrial Myopathy Symptom Assessment