Table 1.

Quality evaluation of studies included in meta-analysis using the Newcastle-Ottawa Scale.

Study	Selection				Comparability	Exposure		HWE
	CD	REC	SC	DC	CCC	AE	SMA
Masson et al., 2008	+	+	+	+	+	+	−	−
Paliwal et al., 2013	+	+	+	+	+	+	+	+
Larusch et al., 2015	+	+	+	+	+	+	−	+
Rosendahl et al., 2018	+	+	+	+	+	+	+	−
Grabarczyk et al., 2017	+	+	+	+	+	+	−	+
Zou et al., 2018	+	+	+	+	+	+	+	+
Hungarian CP cohort	+	+	+	+	+	+	+	+

CD, cases defined adequately; REC, representativeness of the cases; SC, selection of controls; DC, definition of controls; CCC, comparability of cases and controls; AE, ascertainment of exposure; SMA, same method of ascertainment for cases and controls; HWE, Hardy-Weinberg equilibrium in controls.