COPYRIGHT STATEMENTS
The corresponding author has to commit to the Editor-in chief of the Vietnam Journal of Preventive Medicine by the form with following contents:
 - The corresponding author of the research
- All data and results of the research  belong to authors who have named in the research;
- The contents of the research have not been submitted or published elsewhere;
- Be sure that all authors have read the fulltex, and agreed with the order of authors in the article;
- Do not have any conflicts of interest
- The research complied with the ethical aspects of biomedical research.