Methods and definitions: summary

Data presented in the schools survey tables are derived mainly from the ESPAD schools survey project and the HBSC (WHO) Schools survey — Health behaviour in school-aged children. Participation in both surveys, each conducted every four years,has grown in each round and now includes most EU Member States and non-EU countries. The EMCDDA reports ESPAD school survey data from Norway and two candidate countries (Croatia and Turkey).In addition, annual, or biannual, national schools surveys are conducted in Spain, Italy, Portugal and Sweden and regional surveys are conducted in the UK and Belgium.

The international comparability of the ESPAD schools survey is based on nationally representative samples of school classes with the goal of having at least 2400 participating students from the target group, and by standardising the target age group (between 15–16 years), the questionnaire, data collection in schools, assurance of anonymity and the time of year that data collection takes place. Caution is recommended regarding some data in specific countries: comments on these are found in the methodological information sections found on http://www.espad.org and in published reports — ESPAD (The European School Survey Project on Alcohol and Other Drugs) 1995, 1999 and 2003 by The Swedish Council for Information on Alcohol and Other Drugs (CAN) and the Council of Europe (Pompidou Group).

The HBSC (WHO) Health behaviour in school-aged children included, for the first time in the 2001/2002 surveys, questions about cannabis use. International comparability is based on standardisation by target age group (mean age 15.5), cluster sampling methods with the goal of more than 1500 participating students from the target group, questions about cannabis based on the ESPAD survey questionnaire, data collection in the schools, and assurance of anonymity. As with ESPAD, caution is recommended regarding some data in specific countries.Descriptions of the study are found at http://www.hbsc.org and in ‘Young people’s health in context. Health behaviour in school-aged children (HBSC) study: international report from the 2005/2006 survey’ Currie, C. et al (eds.) (2008), Inequalities in young people's health: international report from the HBSC 2005/06 survey. WHO Policy Series: Health policy for children and adolescents. Issue 5, WHO Regional Office for Europe, Copenhagen.

National schools surveys conducted in Belgium, Spain, Italy, Portugal, Slovakia, Sweden and the UKare largely comparable with ESPAD and HBSC surveys in terms of sampling, 15/16-year-old age groups, the questionnaire, data collection in schools, and assurance of anonymity. Overall, the comparisons made between ESPAD data and other school surveys (in three countries — Norway, Sweden and the Netherlands — as well as comparisons between ESPAD and the HBSC surveys) show very similar figures. However, in other countries, differences in methods for achieving prevalence estimates means that caution is necessarywith regard to making direct comparisons between some of these surveys.