Table 3.

Cohort study quality rating (determined using the Newcastle-Ottawa scale).

Study	Year	Selection	Comparability	Outcomes
Cole [13]	2000	****	–	**
Karlsson [34]	2001	****	**	***
Kim [35]	2002	****	–	***
Tjoumakaris [36]	2005	***	–	**
Lützner [37]	2009	***	*	**
Mahiroğulları [38]	2010	***	*	***
Zaffagnini [22]	2012	***	**	***

Assessment strategies: selection (max. 4 stars), comparability (max. 2 stars), and outcome (max. 3 stars).