Table 1.

Risk of bias assessment (Newcastle–Ottawa Quality Assessment Scale criteria for case-control and cross-sectional studies) + case-study assessment.

Study (First Author)	Study Design	Selection					Comparability	Outcome
		Representativeness of the sample		Sample size	Non-respondents	Ascertainment of the exposure	Based on design and analysis	Assessment of outcome	Statistical test
[7]	Cross-sectional	+		+	+	++	-	++
[10]	Cross-sectional	+			+	++	+	++	+
[18]	Cross-sectional	+			+	++	++	++	+
[6]	Cross-sectional	+				++	+	++
[11]	Cross-sectional						-	++
Study (First author)	Study design	Selection					Comparability	Exposure
		Case definition adequate?		Representativeness of the cases	Selection of controls	Definition of controls	Based on design and analysis	Ascertainment of exposure	Same method for cases and controls	Non-response rate
[26]	Case-control	+		+	+	+	+	+	+
[16]	Case-control	+		+	+	+	+	+	+
Study (First author)	Study design	Q1	Q2	Q3	Q4	Q5	Q6	Q7	Q8	Q9
[27]	Case study	√	√	√	x	x	√	x	x	√

- Quality scores for Newcastle–Ottawa scale. Very good studies = 9–10 stars, good studies = 7–8 stars, satisfactory studies = 5–6 stars, and unsatisfactory studies = 0–4 stars [28]. For case-series quality scores: Q1: Was study question or objective clearly stated?, Q2: Was study population clearly and fully described, including case definition?, Q3: Were cases consecutive?, Q4: Were subjects comparable?, Q5: Was intervention clearly described?, Q6: Were outcome measures clearly defined, valid, reliable, and implemented consistently across all study participants?, Q7: Was length of follow-up adequate?, Q8: Were statistical methods well-described?, and Q9: Were results well-described? Good: met 7–9 criteria, Fair: met 4–6 criteria, Poor: met 0–3 criteria.