Table 2

The quality rating of each study based on the Cochrane risk of bias assessment

	Random sequence generation	Allocation concealment	Blinding (participants and personnel)	Blinding (outcome assessment)	Incomplete outcome data	Selective reporting	Other sources of bias
Angeles et al46	Unclear	Unclear	High risk	Unclear	Low risk	Low risk	Low risk
Baird et al45	Unclear	Unclear	Unclear	Unclear	Low risk	Unclear	Low rIsk
Fernald and Gunnar43	High risk	High risk	Unclear	Unclear	Unclear	High risk	High risk
Filmer and Schady52	High risk	High risk	Unclear	Unclear	Low risk	Unclear	Low risk
Kilburn et al40	Unclear	Unclear	Low risk	Unclear	Low risk	Unclear	Low risk
Kilburn et al51	Unclear	Unclear	Unclear	Unclear	Unclear	Low risk	Unclear
Macours et al50	Low risk	Unclear	Unclear	Unclear	Unclear	Low risk	Low risk
Özler et al48	Unclear	Low risk	Unclear	Unclear	Low risk	Low risk	High risk
Ozer et al42	High risk	High risk	Unclear	Unclear	Low risk	Low risk	High risk
Paxson and Schady49	High risk	High risk	Unclear	Unclear	High risk	Unclear	High risk
Shangani et al47	High risk	High risk	Unclear	Unclear	Unclear	Low risk	High risk
Tozan et al39	Unclear	Unclear	Unclear	Unclear	Unclear	Low risk	High risk