Table 2.

The Newcastle-Ottawa scale (NOS).

References	Selection				Comparability	Exposure			Scores
	Adequate definition of cases	Representativeness of the cases	Selection of controls	Definition of controls	Control for important factor	Ascertainment of exposure	Same method of ascertainment for cases and controls	Non-response rate
Hagemeier et al., 2016								–	7
Vasavada et al., 2015			–					–	7
Wu et al., 2019								–	8
Yu et al., 2019								–	8
Murphy et al., 2003			–					–	6
	Selection				Comparability	Outcome
	Representativeness of the exposed cohort	Selection of the non-exposed cohort	Ascertainment of exposure	Demonstration that outcome of interest was not present at start of study	Comparability of cohorts on the basis of the design or analysis	Assessment of outcome	Enough follow-up of cohorts	Adequacy of follow-up of cohorts
Devanand et al., 2010		–		–				–	6
Marigliano et al., 2014		–							7

A study can be awarded a maximum of one star for each numbered item within the selection and exposure categories. A maximum of two stars can be given for comparability.