Table 2.

Study quality assessment

Study	Selection criteria				Comparability	Outcome
	Case definition	Representativeness of the cases	Selection of controls	Definition of controls		Ascertainment of exposure	Same method of ascertainment for cases and controls	Non-respondent rate	Total score
Case-control Studies
Firmino et al. 2016 [30]	★	★	★	★	★	★	★	★	8/9
Vieira-Andrade et al. 2015 [32]	★	★	★	★	★★	★	★	★	9/9
Bendo et al. 2014 [36]	★	★	★	★	★★	★	★	★	9/9
Cross-sectional studies
Soares et al. 2018 [22]	★	★	★	★	★★	★	★	★	9/9
Silva-Oliveira et al. 2018 [23]			★	★	★★	★	★	★	7/9
Martins et al. 2018 [24]	★	★	★		★★	★	★	★	9/9
Ramos-Jorge et al. 2017 [4]		★	★	★	★★	★	★	★	8/9
Neves et al. 2017 [25]	★	★	★	★	★★	★	★	★	9/9
Gonçalves et al. 2017 [26]		★	★		★	★		★	5/9
Gomes et al. 2017 [27]	★	★	★	★		★	★	★	7/9
Bomfim et al. 2017 [28]	★	★	★	★	★	★	★	★	8/9
Pulache et al. 2016 [29]		★	★	★	★★	★	★	★	8/9
Feldens et al. 2016 [31]	★	★	★	★	★★	★	★	★	9/9
Freire-Maia et al. 2015 [33]	★	★	★	★	★★	★	★	★	9/9
Abanto et al. 2015 [34]	★	★	★	★	★★	★	★	★	9/9
Viegas et al. 2014 [5]	★	★	★	★	★★	★	★	★	9/9
Gomes et al. 2014 [35]	★	★	★	★	★★	★	★	★	9/9
Abanto et al. 2014 [37]		★	★	★	★★	★	★	★	8/9
Siqueira et al. 2013 [38]	★	★	★	★	★★	★	★	★	9/9
Dame-Teixeira et al. 2013 [39]	★	★	★		★	★	★	★	7/9
Viegas et al. 2012 [40]		★	★		★★	★	★	★	7/9
Traebert et al. 2012 [41]		★	★	★	★★	★	★	★	8/9
Piovesan et al. 2011 [42]	★	★	★	★	★★	★	★	★	9/9
Aldrigui et al. 2011 [43]			★		★★		★	★	5/9
Bendo et al. 2010 [44]	★	★	★		★★	★	★	★	8/9
Piovesan et al. 2010 [45]	★	★	★	★	★★	★	★	★	9/9

Based on the Newcastle-Ottawa scale (NOS) adapted for observational studies