Table 4.

Results of the risk of bias assessment

Study ID	Reporting	External validity	Internal validity—bias	Internal validity— confounding	Total
Ament et al22	Unclear	High	High	High	High
Benenson et al23	Unclear	High	High	High	High
Cates24	High	Unclear	High	High	High
Enriquez-Puga et al25	Unclear	High	High	Unclear	High
Forsner et al26	Unclear	Low	High	High	High
Gerber et al35	Low	Low	High	High	High
Higuchi et al27	High	High	High	High	High
Kelly28	High	High	High	High	High
Knops et al29	High	Low	High	High	High
Loszadi et al30	Unclear	High	Unclear	High	High
McLaws et al31	High	Low	Unclear	High	High
Stéphan et al32	High	High	Unclear	High	High
Wakefield et al33	High	High	High	High	High
Williams et al34	High	High	Unclear	High	High
Total	High	High	High	High	High