Table 2.

Quality assessment scale for 32 studies

Study	Selection				Comparability		Outcome			Total scores
	Representativeness of the exposed cohort	Selection of the non-exposed cohort	Assessment of exposure	Outcome not present at start of study	Comparability of cohorts on the basis		Assessment of outcome	Follow-up long enough for outcome	Adequacy of follow-up
					Design	Analysis
Yasui	+	+	+		+		+	+	+	7
Fan	+	+	+	+	+	+	+	+	+	9
Conteduca	+	+	+	+	+	+	+	+	+	9
Vidal	+	+	+		+		+	+	+	7
Sun	+	+	+		+	+	+	+	+	8
Uemura	+	+	+		+		+		+	7
Mehra	+	+	+	+	+	+	+	+	+	9
Boegemann	+	+	+		+	+	+	+	+	8
Pei	+	+	+		+	+	+	+	+	8
Buttigliero	+	+	+		+		+	+	+	7
Wang	+	+	+	+	+		+	+	+	7
Jang	+	+	+		+	+	+	+	+	8
Lolli	+	+	+		+	+	+	+	+	8
Shigeta	+	+	+		+		+	+	+	7
Lee	+	+	+		+	+	+	+	+	8
Wang	+	+	+		+	+	+	+	+	8
Langsenlehner	+	+	+		+	+	+	+	+	8
Langsenlehner	+	+	+		+	+	+	+	+	8
Zhang	+	+	+		+		+	+	+	7
Bahig	+	+	+		+	+	+	+	+	8
Lorente	+	+	+		+	+	+	+	+	9
Yao	+	+	+		+	+	+	+	+	8
Li	+	+	+		+		+	+	+	7
McLachlan	+	+	+		+		+	+	+	7
Sharma	+	+	+		+		+	+	+	7
Templeton	+	+	+		+		+	+	+	7
Sonpavde	+	+	+		+	+	+		+	7
Nuhn	+	+	+		+	+	+	+	+	8
Poyet	+	+	+		+		+	+	+	7
Linton	+	+	+	+	+	+	+	+	+	9
Shafique	+	+	+	+	+	+	+	+	+	9
Yamada	+	+	+		+	+	+	+	+	8

A positive result on any one of them was counted as one point