ABSTRACT
This cross-sectional study involved a representative group of students, with ages ranging from 5 to 19 years old (11.8 ± 3.56 mean), from basic and secondary schools in the Valparaiso Region, in Chile. Ten schools were randomly selected from a list given by the Regional Ministerial Secretary of Education and the selection used a cluster design regarding the three types of elementary school administrations in Chile, as well as of the economical background level of the corresponding students.
