The methodology of the Italian Health Behaviour in School-aged Children (HBSC) 2018 study and its development for the next round.

Introduction: The Italian "Health Behaviour in School-aged Children" (HBSC) is a national surveillance system that collects data on health and well-being among adolescents aged 11, 13 and 15 years attending school. It is part of the HBSC Research Network, an international alliance of researchers from 45 European and North American countries and regions started in 1982. Methods: All countries and regions participating in HBSC must adhere to a common international standard protocol developed and systematically updated by the entire HBSC Network. Data collection occurs every four years. Italy joined the international Network in 2000 and, to date, five waves (in 2002, 2006, 2010, 2014 and 2018) have been carried out. From 2010 the Italian HBSC is representative at regional level and in 2017 the base of the "Surveillance system for risk behaviours in 11-17 year-olds" became part of the Prime Ministerial Decree "Identification of surveillance systems and registries of mortality, tumours and other diseases". Cluster sampling is used, with school class as primary sampling unit, and two validated questionnaires are used to collect the information. Results: In 2018, the Italian HBSC involved 3,608 classes and 58,976 students. The average response rates were 86% of sampled classes and 97% of students achieving a national and regional representative sample for youths of all age groups (19,504 eleven-year-old, 20,554 thirteen-year-old and 18,918 fifteen-year-old). The national coordination group prepared a standardized format for disseminating the results locally and indicating areas for intervention A national report and some articles have been published. The next round, which will take place in the 2021-2022 school year, will also involve a representative sample of students of grade four of secondary schools (adolescents aged 17 years) and use on line questionnaires. Conclusions: Over 3 decades at international and 2 decades at national level 35 years have demonstrated that HBSC methodology and its results are useful for monitoring and deepening the knowledge on the most critical issues of adolescents' well-being.