Table 4.

Quality assessment of included studies

Study	Selection bias	Study design	Data-collection methods	Global rating
Abelsen & Olsen26	Moderate	Strong	Strong	Strong
Adams54	Moderate	Strong	Moderate	Strong
Ayers et al.55	Strong	Strong	Strong	Strong
Benicewicz & Metzger56	Moderate	Strong	Moderate	Strong
Blue et al.24	Weak	Weak	Moderate	Weak
Gordon & Rayner57	Moderate	Moderate	Moderate	Strong
Hopcraft et al.25	Moderate	Strong	Moderate	Strong
Kaldenberg & Smith58	Moderate	Strong	Moderate	Strong
Lambert et al.59	Moderate	Strong	Strong	Strong
Moffat & Coates60	Moderate	Strong	Moderate	Strong
Murtomaa & Haugejorden61	Strong	Strong	Moderate	Strong
Sgan-Cohen et al.62	Weak	Weak	Weak	Weak
Van Dam et al.63	Weak	Weak	Weak	Weak
Van Wyk et al.42	Moderate	Strong	Strong	Strong