Apart from the results of the 35 ESPAD countries participating in 2015, data from two more countries are presented in the graphs and tables. These non-ESPAD countries are Spain and the United States. Comparisons with these countries have been performed in previous ESPAD reports as well. This is considered feasible since many of the questionnaire items are identical, or at least very similar. The reason for the many similarities is that the US ‘Monitoring the future’ study has strongly influenced the ESPAD questionnaire.
However, since there are differences both in the overall methodology and, sometimes, in the wording of individual items, caution is called for when results from Spain and the United States are compared with results from the ESPAD countries. To draw attention to this, data from Spain and the United States are presented separately at the bottom of the tables and with divergent patterns in the graphs.
Both Spain and the United States have provided short texts containing information similar to that presented in the ESPAD country reports and summarised in the methodological tables. These presentations are available in Appendices 1 and 2, while some main findings are summarised below.
The Spanish data comes from a long-term series of biennial national school surveys conducted since 1994 by the Spanish Observatory on Drugs and Drug Addiction, which is part of the Governmental Delegation for the National Plan on Drugs (DGPNSD). The data used here were collected between November 2014 and April 2015 among 14- to 18-year-old students (Spanish Observatory on Drugs and Drug Addiction, 2016a, b). Only 15- to 16-year olds are included for ESPAD comparisons (18 280 students). The average age was 15.5 years, hence slightly lower than the ESPAD average of 15.8.
Approximately 83 % of the residents born in 1999 were enrolled in school, and the sampling frame covered almost 100 % of the students. Of the sampled schools, 13 % were replaced due to justified refusals. About 15 % of the students were absent at the time of the survey, while hardly any (0.1 %) declined to take part in the data collection. Fieldwork was performed by research assistants. The Spanish team considers the data collection to have been successful and nationally representative for 15- to 16-year-old students.
The data presented for the United States come from a longterm series of annual national surveys that are part of the ‘Monitoring the future’ project (Johnston et al., 2016; Miech et al., 2015). Three school grades are annually surveyed, but for ESPAD comparisons only the results for grade 10 are compared. The proportion of 10th graders who were 15 years old was 42 %, 16 years old 53 % and 17 years old 5 %. This gives an estimated average age of 16.1 years, which is slightly higher than the ESPAD average of 15.8.
The sample was representative of all 10th grade students in the coterminous United States (48 states, i.e. all except Alaska and Hawaii). About 97 % of the target population were enrolled in school (grade 10) at the time of the data collection, which took place in February-June 2015. Of the sampled schools (original selection and replacement schools) 93 % took part in the study. In the sampled classes 87 % of the students were present and refusals were quite rare (less than 1 %). Fieldwork was performed by research assistants. Approximately 5.1 % of 10th-grade questionnaires were dropped in the 2015 cleaning process due to inconsistencies in sets of answers or non-credible answers. This is a larger proportion of removed questionnaires compared to the ESPAD average of 1.8 %.