Table 2.

Quality assessment of the observational studies

	Ferstl et al[23], n = 115	Kihara and Yokomizo[20], n = 112	Masuda et al[6], n = 11	Sokal et al[14], n = 107	Masuda et al[17], n = 110	Akhtar et al[18], n = 55	Haal et al[21], n = 113	Satake et al[8], n = 101	Doi et al[22], n = 114	Tagashira et al[13], n = 106	Uno et al[12], n = 105	Kogure et al[19], n = 111	Van Lent et al[11], n = 104
Selection
Representativeness of exposed cohort	*	-	*	-	*	*	*	*	*	*	*	*	*
Selection of non-exposed cohort	*	*	*	*	*	*	*	*	*	*	*	*	*
Ascertainment of exposure	*	*	*	*	*	*	*	*	*	*	*	*	*
Demonstration that outcome of interest was not present at start of study	*	*	*	*	*	*	*	*	*	*	*	*	*
Comparability
Comparability of the cohorts	**	-	**	-	**	-	**	**	-	-	**	-	-
Outcome
Assessment of outcome	*	*	*	*	*	*	*	*	*	*	*	*	*
Was follow-up long enough for outcomes to occur?	*	*	*	*	*	*	*	*	*	*	*	*	*
Adequacy of follow-up cohorts	*	*	*	*	*	*	*	*	*	*	*	*	*
Overall	Good	Low	Good	Low	Good	Low	Good	Good	Low	Low	Good	Low	Low

*Represents study meets a criterion in each section of the Newcastle-Ottawa scale; -Represents study meets no criterion in each section of the Newcastle-Ottawa scale.