Table 4. Outcomes of the fixed effects analyses for the primary and secondary outcomes.

Outcome (self-concept)	Studies	Sample size	Fixed effects model			Heterogeneity
			SMD (95% CI)	Z	P	Chi2	df	P	I2
Primary
Average	13	3,348	−0.61 [−0.72, −0.50]	11.35	<.001	55.66	12	<.001	78
Secondary
Reading-Spelling-Writing	5	2,005	−1.13 [−1.32, −0.95]	12.08	<.001	42.60	4	<.001	91
Academic	7	2,598	−0.69 [−0.83, −0.55]	9.39	<.001	22.30	6	.001	73
Math	4	1,902	−0.70 [−0.90, −0.51]	7.19	<.001	11.23	3	.01	73
Global	9	2,049	−0.68 [−0.81, −0.55]	10.42	<.001	37.83	8	<.001	79
Behavioural	2	177	−0.32 [−0.62, −0.03]	2.15	.03	0.07	1	.78	0
School	2	910	−0.59 [−0.86, −0.32]	4.23	<.001	7.26	1	.007	86
Physical Appearance	3	213	−0.28 [−0.55, −0.01]	2.03	.04	1.43	2	.49	0
Work	1	36	−0.23 [−0.89, 0.42]	0.70	0.48
Social	5	869	−0.15 [−0.33, 0.02]	1.73	.08	4.33	4	.36	8
Athletic	2	177	0.15 [−0.15, 0.44]	0.98	0.33	0.92	1	0.34	0
Home	1	1,804	0.31 [−0.29, 0.91]	1.01	0.31