TABLE 2.

Item statistics aggregated by dimension for the reduced IGQ questionnaire

Total population (n = 305)	Eigenvalue	Cumulative variance	Factor loading	Item correlation within scale	Item correlation between scales	Cronbach’s alpha (95% CI)	SEM
Bloating (6 items)	3.33	0.20	0.51‐0.87	0.31‐0.70	0.02‐0.35	0.85 (0.82 ; 0.88)
Flatulence (3)	1.86	0.31	0.58‐0.85	0.43‐0.63	0.02‐0.33	0.76 (0.71 ; 0.81)
Belching (2)	1.65	0.40	0.71‐0.99	0.66	0.05‐0.26	0.80 (0.75 ; 0.84)
Bad breath (2)	1.61	0.50	0.76‐0.96	0.67	0.02‐0.27	0.81 (0.76 ; 0.86)
Stomach rumbling (2)	1.57	0.59	0.63‐0.96	0.63	0.08‐0.32	0.78 (0.72 ; 0.83)
Difficult gas evacuation (2)	1.30	0.67	0.67‐0.78	0.55	0.02‐0.35	0.71 (0.63 ; 0.79)
All 17 items						0.84 (0.81 ; 0.87)	6.44
All items (except bloating) (11)						0.77 (0.72 ; 0.81)	6.16

Confidence interval for Cronbach’s alpha computed by bootstrap. SEM: The standard error of measurement (SEM) has been determined based on Cronbach’s alpha and standard deviation (S), following the relation SEM = S√(1‐R), where R is the reliability defined as the value of Cronbach’s alpha.

Abbreviation: IGQ, Intestinal Gas Questionnaire.