Table 2. Outcomes of the meta-analysis of matched features on transfer.

		Matched feature at training
		Intervention effects								Heterogeneity
Feature category	Transfer feature	k	N	n	d	SE	95% CI	z	p	Q	I2	p
Stimulus type
	Digits	7	7	421	0.994	0.194	0.615–1.374	5.132	< .001	19.397	69.068	< .001
	Letters	5	10	245	0.301	0.142	0.023–0.578	2.123	0.034	4.750	15.791	0.314
	Words/ nonwords	3	4	115	0.568	0.273	0.033–1.103	2.080	0.038	3.952	49.399	0.139
	Objects	2	2	85	0.575	0.222	0.140–1.010	2.590	0.010	0.073	0.000	0.787
	Spatial location	14	26	774	0.551	0.097	0.362–0.740	7.088	< .001	18.770	0.130	0.130
Stimulus domain
	Verbal	19	48	1058	0.455	0.069	0.319–0.591	6.546	< .001	22.691	16.268	0.251
	Visuo-spatial	14	40	681	0.470	0.078	0.316–0.624	0.470	< .001	45.542	69.259	< .001
Stimulus modality
	Auditory	12	21	638	0.470	0.096	0.283–0.658	4.917	< .001	14.924	26.293	0.186
	Visual	21	82	1058	0.459	0.074	0.315–0.603	6.231	< .001	26.501	24.532	0.150
Response modality
	Spoken	2	5	68	0.615	0.253	0.119–1.110	2.431	0.015	0.862	0.000	0.353
	Manual	18	78	1019	0.463	0.077	0.312–0.614	6.021	< .001	26.346	27.883	0.121
Serial recall
	Verbal	9	9	509	0.508	0.095	0.322–0.694	5.355	< .001	8.575	6.709	0.379
	Visuo-spatial	10	10	517	1.054	0.205	0.652–1.456	5.142	< .001	39.318	77.110	< .001
	All	11	19	611	0.709	0.111	0.490–0.927	6.357	< .001	42.525	60.024	< .001
Complex span
	Verbal	6	8	325	0.544	0.175	0.201–0.888	3.110	0.002	10.580	52.743	0.060
	Visuo-spatial	3	4	108	1.010	0.272	0.476–1.544	3.709	< .001	3.471	42.378	0.176
	Cross-domain	3	4	154	0.119	0.267	- 0.405–0.643	0.445	0.656	4.989	59.911	0.083
	All	7	16	423	0.540	0.153	0.241–0.840	3.540	< .001	33.025	66.692	0.001
Backward span
	Verbal	7	7	381	0.778	0.120	.542–1.013	6.470	< .001	7.282	18.722	0.287
	Cross-domain	2	2	161	1.294	0.368	0.572–2.016	3.514	< .001	4.296	76.722	0.038
	All	7	9	381	0.901	0.143	.621–1.181	6.309	< .001	18.853	57.567	0.016

k = number of studies; N = number of effect sizes; n = number of participants