Methods
As described in an earlier publication [17], we conducted
the survey between October and December 2011 in 8
secondary schools in Bremen and Bremerhaven, two cities
in the north of Germany. The participating students were
12–20 years old and attending the 8th grade and above.
We approached the principals of 18 randomly selected
government secondary schools in these two cities and
asked them for permission to conduct the survey in their
schools. Each school was provided with a study flyer in
which the study aims and issues concerning parental consent and data protection were documented. The principals