Table 2.

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

First author	Year	S1	S2	S3	S4	C1a	C1b	E1	E2	E3	OQ
Bieli † [10]	2007	-	*	*	-	*	*	*	*	*	+
Bjornvold [38]	2009	*/-	*	*	*	-	-	NA	NA	-	+/−
Choudhry [40]	2005	-	-	*	-	*	*	-	*	-	+/−
Daley [21]	2009	-	*/-	*	-	-	-	NA	NA	-	+/−
Eder † [25]	2004	-	*	*	-	*	*	*	*	-	+/−
Ege † [22]	2007	-	*	*	-	*	*	*	*	*	+
Fageras Bottcher † [39]	2004	*	-	-	-	*	*	*	*	-	+/−
Genuneit [46]	2009	-	*	*	*/-	*	-	NA	NA	-	+/−
Heinzmann [12]	2003	*	*	*	-	-	-	NA	NA	-	+/−
Heinzmann [58]	2010	*	-	*	-	-	-	NA	NA	-	+/−
Hoffjan [61]	2005	-	-	-	*	-	-	NA	NA	-	–
Hussein [59]	2012	*	*	-	*	-	-	NA	NA	-	+/−
Jackola [23]	2006	*	-	*	*	*	-	NA	NA	-	+/−
Kabesch † [13]	2004	-	*	*	-	-	-	NA	NA	-	+/−
Kormann§ [27]	2008	*	*	*	*	*	-	NA	NA	-	+
Kurowski [44]	2011	-	-	*	-	-	-	*	*	-	–
Marcos [50]	2010	*	-	-	*	-	-	*	-	-	–
Miedema§ [45]	2012	-	-	*	*	-	-	NA	NA	-	+/−
Moller-Larsen [28]	2008	*	-	*	*	*	-	NA	NA	-	+/−
Perin [42]	2011	*	-	-	*	-	-	NA	NA	-	+/−
Puthothu [57]	2006	*	-	*	-	-	-	NA	NA	-	+/−
Schubert [60]	2006	*	-	*	-	-	-	NA	NA	-	+/−
Sengler § [37]	2003	-	*	*	*	*	-	NA	NA	-	+/−
Snijders † [52]	2006	-	*	*	*	*	*	*	*	-	+
Sorensen § [47]	2009	-	*	*	*	*	*	*	*	*	+
Tremblay [20]	2008	-	*/-	*	-	-	-	NA	NA	-	+/−
Yang [55]	2004	-	-	*	*	*	*	NA	NA	-	+/−
Zhang [43]	2011	*	*	*	*	*	*	*	*	-	+

S1: Case definition; S2: Representativeness of the cases; S3: Selection of controls; S4: Definition of controls; C1a/C1b Comparability of cases and controls on the basis of the design or analysis; E1: Ascertainment of exposure; E2: Same method of ascertainment for cases and controls; E3: Non-response rate (*: criteria were met; -: criteria were not met); OQ: Overall quality (+: better than average quality, +/− average quality, – less than average quality); † cross-sectional study; § nested case control study; NA = not applicable.