Table 2.

The quality assessment of 12 included studies based on the Newcastle–Ottawa Scale (range 0–9).

Study	Representativenessof the exposedcohort	Selection of thenon-exposedcohort	Ascertainment ofexposure	Demonstration thatoutcome of interestwas not present atstart of study	Comparability ofcohorts on the basisof the design oranalysis	Assessment of outcome	Was follow-uplong enough foroutcomes tooccur	Adequacy offollow up ofcohorts	Quality score
Paparodis (21)	*	*	*	*	**	*	*	*	9
Dubrarka (25)	*	*	*	*	*	*	*	*	8
Jackson (26)	*	*	*	*	*	*	*	*	8
Mukasa	*	*	*	*	*	*	*	*	8
Chen (30)	*	*	*	*	*	*	*	*	8
Morais (31)	*	*	*	*	*	*	*	*	8
Holm (32)	*	*	*	*	*	*	*	*	8
Liu (33)	*	*	*	*	*	*	*	*	8
Anil (34)	*	*	*	*	*	*	*	*	8
Consorti (36)	*	*	*	*	*	*	*	*	8
Konturek (37)	*	*	*	*	*	*	*	*	8
Dailey (38)	*	*	*	*	*	*	*	*	8