Knowledge about levels of alcohol and drug use can be obtained in different ways, depending on the part of the phenomenon that is of main interest. In many countries, household surveys are conducted to measure substance use habits in the general population. School surveys are also often performed, either as a complement to other investigations or as the only investigative measure.

One problem with surveys is that they usually fail to reach some segments of the population, such as problematic users, homeless persons or dropouts from school. The latter is a group of young people vulnerable to substance use.

The main rationale for carrying out school surveys is that students are at an age when onset of the use of different substances is likely to occur and its monitoring is therefore important. Another reason is ease of access: students, by definition, are to be found within the school system, which reduces the cost of locating and reaching them. Yet another advantage is that the response rates normally are high. It is unusual for students who are present in the classroom to refuse to take part in surveys.

When students are the target group of a survey, it is a wellaccepted method to use group-administered questionnaires in a classroom setting where data are collected under the same conditions as a written test. While it is true that experiences from using school surveys to collect information on substance use may differ across countries, there is usually no other realistic way of collecting data from students than to do so by administering questionnaires to a group in the school, usually in the classroom.