Table 3.

Quality assessment of included prospective and retrospective cohort studies

Study	Representativeness of the exposed cohort	Selection of the non-exposed cohort	Ascertainment of exposure	Demonstration that outcome of interest was not present at start of study	Comparability of cohorts on the basis of the design or analysis controlled for confounders	Assessment of outcome	Was follow-up long enough for outcomes to occur	Adequacy of follow-up of cohorts
Diracoglu et al. [18]	1 star	1 star	1 star	–	1 star	1 star	1 star	1 star
Ohnuki et al. [17]	1 star	1 star	1 star	–	1 star	1 star	1 star	1 star