Monitoring health and health behaviors among adolescents in Central Catalonia: DESKcohort protocol Judit Rogés; Helena González-Casals; Marina Bosque-Prous; Cinta Folch; Joan Colom; Jordi Casabona; Gemma Drou-Roget; Ester Teixidó-Compañó; Esteve Fernández; Carmen Vives-Cases; Albert Espelt;