Table 4.

The table shows the risk of bias criteria using the adapted Newcastle Ottawa Scale (NOS) for cross-sectional studies. If the criterion is met, a green dot is placed in the box, otherwise, if it is not met, a red dot is placed. Studies with a total score of 7 or 8 green points were considered a low risk of bias; 6 green dots were considered to be at medium risk of bias; 5 green dots or less were judged to be at high risk of bias.

Item	Saminsky, M. et al., 2015 [30]	Goh, V. et al., 2017 [22]	De Beule, F. et al., 2017 [21]	D’Aiuto, F. et al., 2005 [20]	Graetz, C. et al., 2017 [24]	Machtei, E. & Hirsch, I., 2007 [28]	Bäumer, A. et al., 2011 [19]	Graetz, C. et al., 2011 [23]	Martinez-Canut, P., 2015 [29]
Selection
1.Is the sample representative of the target average population?
2.Was the sample size justified and satisfactory?
3.It was established which subjects would be included and was the inclusion range satisfactory?
Comparability
1.Were anthropometric measurements adequately adjusted for age and gender?
2.Were other factors such as race/ethnicity, educational level, habits, probing depth, survival rate, etc. adequately adjusted?
Results
1.Was the result established independently and with data linkage?
2.Was the result determined by a self-report?
3.The statistical test used to analyze the information is clearly described and appropriate, and the measures of the association presented include confidence intervals and level of probability (p-value)?
Total	6	6	7	4	6	7	7	8	7