Table 1.

Quality scoring based on the Newcastle-Ottawa quality assessment scale: cohort studies

First author	Year	S1	S2	S3	S4	C1a	C1b	O1	O2	O3	OQ
Bieli † [10]	2007	*	*	*	-	*	*	-	*	-	+/−
Bottema [26]	2010	*	*	NA	*	-	-	-	*	-	+/−
Custovic [62]	2011	*	*	-	*	*	*	-	*	*	+
Eder † [25]	2004	*	*	*	-	*	*	-	*	-	+/−
Ege † [22]	2007	*	*	*	-	*	*	-	*	-	+/−
Fageras Bottcher † [39]	2004	-	*	*	-	*	*	*	*	-	+/−
Guerra [11]	2004	*	*	-	*	*	*	-	-	-	+/−
Jones [48]	2002	-	*	NA	*	-	-	-	-	-	–
Kabesch † [13]	2004	*	*	NA	*	-	-	-	*	-	+/−
Kerkhof [56]	2010	*	*	*	*	*	*	-	*	-	+
Lange [63]	2011	*	*	NA	-	*	*	*	*	-	+
Lodrup Carlsen [51]	2010	*	*	NA	*	*	*	-	*	*	+
O’Donnell [36]	2004	*	*	NA	-	*	*	-	*	*	+
Reijmerink [41]	2010	*	*	NA	*	-	-	-	*	-	+/−
Rothenbacher [53]	2005	*	*	*	*	*	*	-	-	*	+
Simpson [8]	2006	*	*	*	*	*	*	-	*	*	+
Snijders † [52]	2006	*	*	*	*	*	*	-	-	*	+
Soferman [54]	2004	-	*	NA	*	*	*	*	*	*	+

S1: Representativeness of the exposed cohort, S2: Selection of non-exposed cohort, S3: Ascertainment of exposure, S4: Outcome of interest not present at start of study, C1a/C1b: Comparability of cohorts on the basis of the design or analysis, O1: Assessment of outcome, O2: Duration of follow-up, O3: Adequacy of follow up (*: criteria were met; -: criteria were not met); OQ: Overall quality (+ better than average quality, +/− average quality, – less than average quality); NA = not applicable; † cross-sectional study.