Table 2.

Methodological quality assessment using the Newcastle-Ottawa scale [12]

Cohort studies
	Selection				Comparability	Outcome
	Representativeness of exposed cohort	Selection of non exposed cohort	Ascertainment of exposure	Demonstration outcome not present at start of study	Comparability of cohorts	Ascertainment of outcome	Follow-up long enough for outcomes to occur	Adequacy of follow up of cohorts
Alam et al. [14] (2011)	★	★	★	★		★	★	★
Alam et al. [13] (2013)	★	★	★	★		★	★	★
Baldwin et al. [24] (1991)	★	★	★	★	★★	★	★	★
Birkeland et al. [15] (2013)	★	★	★	★	★★	★	★	★
Bismark et al. [38] (2013)	★	★	★	★	★★	★	★	★
Donaldson et al. [39] (2014)	★	★	★	★		★	★	★
Elkin et al. [18] (2011)	★	★	★	★	★	★	★	★
Ely et al. [26] (1999)	★	★	★	★	★★	★	★	★
Goldenbaum et al. [36] (2008)	★	★	★	★		★	★	★
Hickson et al. [27] (2002)	★	★	★	★	★★	★	★	★
Khaliq et al. [19] (2005)	★	★	★	★	★★	★	★	★
Pande et al. [37] (2013)	★	★	★	★		★	★	★
Papadakis et al. [20] (2008)	★	★	★	★	★★	★	★	★
St George[32] (2003)	★	★	★	★		★	★	★
Tamblyn et al. [33] (2007)	★	★	★	★	★★	★	★	★
Taragin et al. [28] (1992)	★	★	★	★	★	★	★	★
Weycker et al. [30] (2000)	★	★	★	★	★★	★	★	★
Case-control and Cross-sectional studies
	Selection				Comparability	Exposure
	Case definition	Representativeness of cases	Selection of controls	Definition of controls	Comparability of cases and controls	Ascertainment of exposure	Method of ascertainment for cases and controls	Non-response rate
Cardarelli et al. [16] (2004)	★	★	★	★	★★	★	★	★
Clay et al. [17] (2003)	★	★	★	★	★★	★	★
Kohatsu et al. [6] (2004)	★	★	★	★	★★	★	★
Morrison et al. [7] (1998)	★	★	★	★	★★	★	★	★
Papadakis et al. [8] (2004)	★	★	★	★	★★	★	★
Papadakis et al. [9] (2005)	★	★	★	★	★★	★	★	★
Yates et al. [22] (2010)	★	★	★	★	★★	★	★
Balch et al. [23] (2011)			★	★	★★		★
Chauhan et al. [25] (2005)		★	★	★	★★		★
Nash et al. [35] (2009)			★	★	★★		★
Nash et al. [34] (2009)	★		★	★			★
Unwin et al. [5] (2014)	★	★	★	★	★★	★	★	★
Wakeford et al. [21] (2011)	★	★	★	★		★	★	★
Weisman et al. [29] (1988)		★	★	★	★★		★
Wu et al. [31] (2009)		★	★	★	★★		★