Table 2.

Risk of bias within cohort studies

Source	Selection bias	Information bias	Confounding	Appropriate sample size	Appropriate analytic strategies
Emtner M et al. 1998	Low risk	Low risk	Low risk	Unclear risk	Appropriate
Emtner M et al. 1996	Low risk	Low risk	Low risk	Unclear risk	Appropriate
Engstom I, et al. 1991	Unclear risk	Low risk	Low risk	Unclear risk	Appropriate
Juvonen R, et al. 2008	Low risk	Low risk	Low risk	Unclear risk	Appropriate
Newcomb, P. et al. 2012	Unclear risk	Low risk	Low risk	Unclear risk	Appropriate
Nickerson BG et al., 1983	Low risk	Low risk	Low risk	Unclear risk	Appropriate
Silva PL, et al. 2011	Low risk	Low risk	Low risk	Low risk	Appropriate