Table IV.

Study quality as assessed by the Newcastle Ottawa Scale

Study	Selection (maximum, 4 asterisks)	Comparability (maximum, 2 asterisks)	Exposure (maximum, 3 asterisks)	Total score	Level
Coughlin et al. 2004	***	**	**	7	2
Sasanabe et al. (male) 2006	**	**	***	7	2
Sasanabe et al. (female) 2006	**	**	***	7	2
Gruber et al. 2006	**	**	***	7	2
Nieto et al. 2009	***	**	***	8	2
Chin et al. 2010	**	**	**	6	2
Muraki et al. (male) 2010	***	*	**	6	2
Muraki et al. (female) 2010	***	*	**	6	2
Troxel et al. 2010	***	*	**	6	2
Theorell-Haglow et al. 2011	***	**	***	8	2
Gasa et al. 2011	**	**	***	7	2
Agrawal et al. 2012	**	**	***	7	2
Hall et al. 2012	***	**	***	8	2