Methodological improvements over time are inevitable. For each data collection some changes have been made to the master questionnaire. It may be necessary to make amendments due to realities that did not exist in the past, for example the introduction of new substances on the market. In 2015, questions regarding harm from other people’s drinking, use of new psychoactive substances, money gambling and internet use was added in the core section of the questionnaire. To make room, questions related to alcohol purchases, drinking locations and expected consequences of alcohol consumption were removed. Another change was that the questions on use of amphetamines, cocaine and crack were lifted from the list of various illicit substances used and introduced as separate questions. In addition, a separate question on methamphetamines was introduced.
In 2007, several structural changes were made to the questionnaire, and for some of the substance use measures the specific questions were altered. In order to evaluate the comparability of estimates based on the old and the new versions of the questionnaire, a methodological study based on a split-half methodology was conducted in 2006 in eight countries (Hibell and Bjarnason, 2008). Overall, it was found that the changes to the instrument did not affect the key indicators used to track changes in adolescent substance use over time. The estimates that turned out to have been significantly affected by the changes were primarily those that were based on problematic measures and had therefore been purposely changed in order to obtain better estimates. They included measures of the availability of different substances, the frequency of intoxication, the amount of alcohol consumed during the most recent drinking day and spirit consumption during the past 30 days. For these variables, comparisons thus cannot be made with data from 1995-2003, which is indicated in the relevant tables. Please refer to the previous ESPAD reports to find out more about historical questionnaire changes.
There was no such split-half study performed in relation to the changes to the 2015 questionnaire. This was not considered necessary since none of the questions related to substance use were rephrased and most of the new questions were located towards the end of the questionnaire. It could however be mentioned that the changes made in the master questionnaire led to an increase in the number of core items, from 173 in 2011 to 213 in 2015. All master ESPAD questionnaires from 1995-2015 are available online (http://www.espad.org).