Table 2.

Subgroup analyses of all sleep indexes.

Sleep indexs	Variable	No. of studies	Sample size	SMD (95%CI)	Test for overall effect		Heterogeneity		p value for subgroup difference
					Z	p value	I2	p value
PSQI	Country								0.27
	US	5	107	−1.05 (−1.89, −0.21)	2.44	0.01	72%	<0.01
	Other countries	4	278	−0.45 (−1.11, 0.22)	1.32	0.19	85%	<0.01
	The number of participants								0.37
	<50	6	130	−0.93 (−1.60, −0.25)	2.69	<0.01	66%	0.01
	≥50	3	255	−0.44 (−1.25, 0.38)	1.05	0.29	90%	<0.01
	Duration								0.97
	<4 weeks	5	225	−0.73 (−1.53, 0.07)	1.79	0.07	84%	<0.01
	≥4 weeks	4	160	−0.76 (−1.57, 0.06)	1.82	0.07	79%	<0.01
Total sleep time	Country								0.26
	US	3	79	−0.20 (−0.69, 0.29)	0.79	0.43	15%	0.31
	Other countries	3	246	0.12 (−0.13, 0.38)	0.94	0.35	4%	0.35
	The number of participants								0.26
	<50	3	79	−0.20 (−0.69, 0.29)	0.79	0.43	15%	0.31
	≥50	3	246	0.12 (−0.13, 0.38)	0.94	0.35	4%	0.35
	Duration								0.5
	<4 weeks	2	165	0.16 (−0.31, 0.63)	0.67	0.50	52%	0.15
	≥4 weeks	4	160	−0.04 (−0.38, 0.31)	0.22	0.83	12%	0.33
Sleep efficiency	Country								0.67
	US	3	79	0.20 (−0.51, 0.90)	0.54	0.59	57%	0.10
	Other countries	2	194	0.03 (−0.25, 0.31)	0.21	0.83	0%	0.77
	The number of participants								0.67
	<50	3	79	0.20 (−0.51, 0.90)	0.54	0.59	57%	0.10
	≥50	2	194	0.03 (−0.25, 0.31)	0.21	0.83	0%	0.77
	Duration								0.55
	<4 weeks	1	113	−0.01 (−0.37, 0.36)	0.03	0.98	NA	NA
	≥4 weeks	4	160	0.17 (−0.27, 0.61)	0.76	0.45	40%	0.17

NA, Not available.