Table 2.

Study quality

Criteria		Yes
1	Was the research question or objective in this paper clearly stated?	48/48
2	Was the study population clearly specified and defined?	48/48
3	Was the participation rate of eligible persons at least 50%?	17/48
4	Were all the subjects selected or recruited from the same or similar populations (including the same time period)? Were inclusion and exclusion criteria for being in the study pre-specified and applied uniformly to all participants	48/48
5	Was the study population similar to the national population?	14/48
6	Was the sampling methods specified and appropriate?	48/48