Table 6.

Quality assessment of case–control studies for α-synuclein and DJ-1 according to the customized Newcastle–Ottawa Scale (NOS).

Criteria		1 [28]	2 [29]	3 [30]	4 [31]	5 [32]	6 [33]	7 [34]	8 [35]	9 [36]	10 [37,38]	11 [39]	12 [40]	13 [41]	14 [42]
Selection	Representativeness of the sample	*	*	-	*	*	*	*	*	*	*	*	*	*	*
	Sample size	-	-	-	-	-	-	-	-	-	-	-	-	*	-
	Non-respondents	-	-	-	-	-	-	-	-	-	-	-	-	-	-
	Ascertainment of the exposure (risk factor)	*	*	-	*	*	*	*	*	*	*	*	*	*	*
Comparability	Subjects in different outcome groups are comparable (confounding factors controlled)	(*) (*)	(*) (-)	(*) (*)	(*) (-)	(*) (-)	(*) (*)	(*) (-)	(*) (*)	(*) (*)	(*) (*)	(*) (-)	(*) (-)	(*) (*)	(*) (*)
Outcome	Assessment of the outcome	*	*	-	*	*	*	*	*	*	*	*	*	*	*
	Statistical test	*	*	*	*	*	*	*	*	*	*	*	*	*	*
	Total Score	6	5	3	5	5	6	5	6	6	6	5	5	7	6
	Quality	fair	fair	poor	fair	fair	fair	fair	fair	fair	fair	fair	fair	good	fair
	Risk of Bias	mod	mod	high	mod	mod	mod	mod	mod	mod	mod	mod	mod	low	mod

* Criteria fulfilled, - Criteria not fulfilled.