Sociodemographic variables (4 questions) selected for
this study were: gender, age, and monthly school tuition
(obtained directly from schools’ principals) and economic
scale [35], considering educational level of the
head of the household, number of household goods
(such as television, DVD players, cars, refrigerators, etc)
and number of housekeepers. This scale classifies students
from A to E (where A is the highest economic
strata). Private school monthly tuition fees were subdivided
in quartiles as: US$ 100-190; US$ 191-260; US$
261-480, US$ 481-1300.