Table 4. Subgroup analyses of the association between the TGF-β plasma levels and incidence of AF.

Subgroup	Study	Number of studies	Heterogeneity		Meta-analysis
			I2	p-Value	SMD	95% CI	p-Value
Follow-up duration	<12 months	2	0%	0.49	0.48	[0.04, 0.92]	0.03
	≥12 months	5	88%	<0.00001	0.36	[-0.19, 0.92]	0.2
Study design	Cohort	7	83%	<0.00001	0.38	[-0.05, 0.81]	0.09
	Case control	5	95%	<0.00001	1.07	[0.26, 1.89]	0.01
LVEF	<50%	2	0%	0.61	0.07	[-0.25, 0.39]	0.67
	≥50%	8	92	<0.00001	0.81	[0.36, 1.26]	0.0004
Sample size	<100	8	92%	<0.00001	1	[0.24, 1.75]	0.01
	≥100	4	48%	0.12	0.17	[-0.02, 0.35]	0.07
Age of patients	≤50 years	4	97%	<0.00001	1.75	[0.09, 3.41]	0.04
	>50 years	8	57%	0.02	0.25	[0.01, 0.48]	0.04

AF = atrial fibrillation; LVEF = left ventricular ejection fraction; CI = confidence interval; SMD = standard mean difference.