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 4 Item loadings and factor correlations from exploratory factor analyses of the PMMSA items, for both the 10-item TSS and 4FS

Item	F1	F1	F2		F1	F2	F3
TSS
Tiredness at rest	0.88	0.93	− 0.07		− 0.15	− 0.93	0.12
Tiredness during activities	0.89	0.92	− 0.03		− 0.03	− 0.92	− 0.02
Muscle weakness at rest	0.92	0.92	0.01		0.01	− 0.92	− 0.02
Muscle weakness during activities	0.94	0.86	0.13		0.16	− 0.86	− 0.02
Balance problems	0.62	0.62	0.01		0.30	− 0.54	− 0.18
Vision problems	0.16	0.04	0.18		0.29	0.03	0.10
Abdominal discomfort	0.37	0.02	0.58		0.16	− 0.05	0.66
Muscle pain	0.57	− 0.01	0.89		0.49	− 0.13	0.42
Numbness	0.45	0.07	0.60		0.87	− 0.01	0.02
Headache	0.28	− 0.02	0.49		− 0.06	0.00	0.80
		Factor correlations			Factor correlations
			F1	F2		F1	F2	F3
		F1	1		F1	1
		F2	0.55	1	F2	− 0.43	1
					F3	0.23	0.32	1

Item	F1	F1	F2
FS
Tiredness at rest	0.90	0.01	− 1.01
Tiredness during activities	0.90	0.47	− 0.49
Muscle weakness at rest	0.92	0.57	− 0.40
Muscle weakness during activities	0.92	1.03	0.04
		Factor correlations
			F1	F2
		F1	1
		F2	− 0.78	1

Bold text indicates factor loadings larger than 0.40 in absolute value
CEFA = categorical exploratory factor analysis; PMMSA = Primary Mitochondrial Myopathy Symptom Assessment
The CEFA is based on scores combined 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]). Nesting was intentionally ignored. Additionally, in instances in which a response category had less than five observed responses, the responses were recoded as the next lowest response category except for the response option 0-Not at all, which was recoded as the next highest response category. For the CEFA of the 10-item PMMSA, solutions with up to three factors were examined, while a maximum of two factors were used for the Fatigue 4 scale subset. An item was considered to belong to a factor if the loading value was greater than 0.40 in absolute magnitude