Methods
Design and data collection
This was a cross sectional study conducted on 9–10 years old female students (grade four) in
Rasht (a metropolitan in north Iran) in 2012. For the data collection a list of all governmental
female schools were provided (66 schools) and a systematic random sampling was applied
(one out of 3 schools) in order to insure that every region in the city represent in the study.
The estimated number of students sampled from each school was based on the fact that we
thought for factor analysis at least a sample of 250 students is needed (50 students per each
main construct of the Health Belief Model). Usually there were 20 to 25 grade four students
within each school. Then, within each school 12 students were recruited by a simple random
sampling approach (with one exception where 13 students were recruited). In each school
students were asked to respond to the study questionnaire. They were free to reject the
invitation. Fortunately all students accepted the invitation and participated in the study. The
main investigator was present to help students while they were responding to the
questionnaire. Due to regulations since the main investigator was female she was not allowed
to attend to the boys’ schools.