The standardisation of survey methodology is the cornerstone of the ESPAD project. However, it should be stressed that standardisation alone does not ensure that data are directly comparable between countries. It is not possible to control for everything, and indeed some influences are not even possible to pinpoint. The cultural contexts in which the students have responded vary, and formally identical measures may have different meanings in different contexts.
As part of the preparations for the ESPAD 1999 datacollection exercise, a methodological study was conducted to better ascertain the role of cultural context in different countries (Hibell et al., 2000). Data were collected in countries in different parts of Europe: two northern European countries (Denmark and Sweden), two Mediterranean countries (Cyprus and Malta) and three in central and eastern Europe (Lithuania, Slovakia and Ukraine). The study showed that both reliability and validity were high in all seven countries, even though there were some minor differences. This indicates that the influence of the cultural context seemed to be rather limited in these seven countries, but even so it is important to keep this aspect in mind when comparing results from a large number of countries.
One of the important long-term goals of the ESPAD project is to track changes in adolescent substance use over time. While cultural context may affect the validity of responses to formally standardised measures, changes in such responses over time may be relatively less affected by the cultural context (which can be expected to be reasonably stable over time in a given country). In other words, even if the proportions using a particular substance are not fully comparable between two countries, it is still possible to compare those countries with regard to the extent of increases or decreases over time in those proportions.