Table 4.

Newcastle-Ottawa Scale assessment of studies included in the meta-analysis.

Study (year)	Selection				Comparability		Exposure			Total Score	Quality
	Case definition adequate	Representativeness of the cases	Selection of controls	Definition of controls	Adjustment for age	Adjustment for other factors	Ascertainment of exposure	Uniform method of ascertainment	Non-response rate
Hviid (2004)	*	*	*	*	–	–	*	*	*	7	High
Szmigiel (2007)	*	*	*	*	–	–	*	*	*	7	High
Szmigiel (2009)	*	*	*	*	–	*	*	*	*	8	High
Nardi (2012)	*	*	*	*	–	–	*	*	–	6	Low
Enghelabifar (2014)	*	*	*	*	–	–	*	*	*	7	High
Lashley (2014)	*	*	*	*	–	*	*	*	*	8	High
Dahl (2014)	*	*	*	*	–	–	*	*	*	7	High
Nardi (2016)	*	*	*	*	–	–	*	*	*	7	High
Craenmehr (2019)	*	*	*	*	–	–	*	*	*	7	High
Nowak (2020)	*	*	*	*	–	–	*	*	*	7	High
Nilsson (2020)	*	*	*	*	–	–	*	*	*	7	High

*denotes one score.