Table 1.

Factor loadings obtained by principal component analysis and confirmatory factor analysis of the present study

Domain	Item number	Item wording	Factor loadings
			Study (PCA)	Study (CFA)	Sedaghat (PCA)	Fenga (CFA)	Fengb (CFA)
Nasal symptoms
	1	Need to blow your nose	0.86	0.85	0.85	0.75	0.64
	2	Sneezing	0.63	0.65	0.75	0.67	0.64
	3	Running nose	0.84	0.71	0.80	0.67	0.57
	4	Cough	0.43*	0.74	0.65	0.59	0.57
	5	Post-nasal discharge	0.60	0.47*	0.60	0.73	0.76
	6	Thick nasal discharge	0.77	0.48*	0.70	0.85	0.77
	21	Difficulty to feel ‘smells’ or ‘tastes’	0.51	0.63	0.45*	0.52	0.35*
	22	Stuffed nose	0.76	0.74	0.60	0.89	0.76
Otologic symptoms
	7	A feeling of full or stuffed ear	0.83	0.80	0.85	0.77	0.72
	8	Dizziness or vertigo	0.77	0.70	0.65	0.83	0.64
	9	Earache	0.82	0.66	0.85	0.71	0.62
	10	Facial pain or pressure	0.49 *	0.47 *	0.60	0.80	0.84
Sleep symptoms
	11	Difficulty sleeping	0.89	0.84	0.70	0.74	0.66
	12	Wake up in the middle of the night	0.90	0.87	0.80	0.75	0.62
	13	Lack of a good night’s sleep	0.92	0.95	0.95	0.76	0.65
	14	Wake up tired	0.73	0.73	0.85	0.83	0.77
	15	Fatigued or tired during the day	0.69	0.75	0.80	0.83	0.77
	16	Reduced productivity	0.79	0.89	0.65	0.88	0.75
	17	Reduced concentration	0.79	0.78	0.65	0.90	0.84
	18	Frustrated, restless or irritated	0.81	0.84	0.60	0.92	0.87
Emotional symptoms
	19	Sadness	0.79	0.53	0.75	0.92	0.87
	20	A feeling of shame	0.50	0.69	0.75	0.67	0.66

For comparison, the previously proposed four-domain structure and its corresponding factor loadings were collected [23, 24]

Bold items loaded more clearly to other domains in the principal component analysis performed in this study as compared to the previously proposed four-domain structure by Sedaghat [24]

*Item with low factor loading < 0.5

^aData from Boston cohort as provided by Feng and co-authors [23]

^bData from Reno cohort as provided by Feng and co-authors [23]