Table 4.

Newcastle Ottawa Scores for the cross-sectional studies

Reference	Selection				Comparability	Outcome		Quality of research
	Representativeness of the sample	Sample size	Non-respondents	Ascertainment of exposure		Assessment of the outcome	Statistical test
Salem et al.37 1984	c	b	b	a**	b*	b**	b	Low
Amer et al.38 1985	b*	a*	b	b*	b*	b**	a*	Moderate
Saleh et al.39 2017	b*	a*	b	b*	b*	b**	b	Low

Representativeness of the sample: a) Truly representative of the average in the target population, all subjects or random sampling*, b) Somewhat representative of the average in the target population, non-random sampling*, and c) Selected group of users. Sample size: a) Justified and satisfactory*, and b) Not justified. Non-respondents: a) Comparability between respondents and non-respondent characteristics is established, and the response rate is satisfactory*, and b) The response rate is unsatisfactory, or the comparability between respondents and non-respondents is unsatisfactory. Ascertainment of the exposure (risk factor): a) Validated measurement tool**, and b) Non-validated measurement tool, but the tool is available or described*. Comparability (maximum 2 stars): b) The study control for any additional factor*. Outcome (maximum 3 stars): b) Record linkage**. Statistical test: a) The statistical test used to analyze the data is clearly described and appropriate, and the measurement of the association is presented, including confidence intervals and the probability level (p-value)*, and b) The statistical test is not appropriate, not described or incomplete.