Table 1.

List of items extracted from each paper

1.	Name of authors
2.	Country
3.	Title of paper
4.	Source
5.	Objective of study (and if NP was the primary objective)
6.	Study design (cross-sectional or longitudinal)
7.	Method of data collection (questionnaire, interview, or examination)
8.	Sampling method and sample data (age, sex, target and final sample, and response rate)
9.	Description of NP (definition, type and validation of questionnaire)
10.	Outcome data (type of prevalence, gender, age, prevalence, 95% CI)
11.	Quality score (based on seven equally weighted quality criteria)
12.	Own remarks or conclusion