Effect of theta-transcranial alternating current stimulation on working memory performance among healthy adults: A systematic review and meta-analysis

Table 2 N-back subgroup analyses

Covariables	Subgroups	Number of effect sizes	Hedges’ g	95%CI	I² (%)	τ²	P value
Study design							0.296
	Within-subject	33	0.260	0.136-0.386	57.20	0.079
	Between-subject	8	0.504	0.064-0.945	64.80	0.268
Target region							0.681
	Frontoparietal	18	0.324	0.096-0.552	72.50	0.181
	Parietal	9	0.200	-0.012 to 0.412	39.30	0.039
	Frontal	14	0.306	0.128-0.485	41.20	0.035
Frequency							0.001
	Fixed	15	0.608	0.336-0.881	72.30	0.204
	Personalized	26	0.133	0.039-0.227	11.70	< 0.001
Concurrent task							0.014
	Online	15	0.490	0.239-0.742	67.3	0.167
	Offline	20	0.153	0.057-0.250	36.80	0.004
Load							0.726
	1	4	0.532	-0.032 to 1.097	69.80	0.227
	2	18	0.274	0.041-0.508	73.60	0.192
	3	15	0.251	0.131-0.371	26.50	< 0.001
	4	2	0.549	0.005-1.094	21.60	0.033
	5	2	0.187	-0.283 to 0.657	0.00	0.000
Task modality							0.005
	Spatial	3	1.168	0.529-1.807	77.90	0.245
	Verbal	36	0.189	0.096-0.281	35.40	0.014
	Objective	2	0.405	0.143-0.666	0.00	0.000

CI: Confidence interval.