This description was provided by the Spanish Observatory on Drugs and Drug Addiction.

The Spanish data presented in this report come from a longterm 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). 2014 survey data were collected by Análisis e Investigación, SL. Data analysis was performed by the Spanish Observatory on Drugs and Drug Addiction (Rosario Sendino, principal researcher; Aurora Ruiz, Noelia Llorens, Begoña Brime and Elena Álvarez, co-principal researchers). In all, nearly 300 000 students from approximately 7 000 schools have been surveyed over the life of the study.

Ethical procedures

The participation of students in the Spanish survey was based on passive parental consent, as parents’ associations of schools, school administrations and regional educational authorities were informed about the nature, objectives and characteristics of the study.

Since the Spanish national school survey is a part of the Spanish national statistical plan, it is compulsory for schools to participate unless they have serious and justified grounds for refusing. All selected students were informed that participation in the survey was voluntary. To ensure confidentiality, all questionnaires were anonymous. Field researchers were responsible for the data collection. Teachers were invited to stay in the classrooms during the administration of the survey, but their role was limited to assisting fieldworkers in keeping the group working in silence and order.

Population, sampling and representativeness

The reference population was the 1 489 531 students aged 14-18 attending public and private schools of secondary, highschool and vocational education. Schools for students with special needs and specialised study subjects such as arts or music were excluded. The sample consisted of 37 486 students aged 14-18 who attended secondary school in all regions of Spain in 2014, including urban and rural as well as public and private schools. These students represented 70 % of all youths of this age in Spain. School is compulsory in Spain until the age of 16. Approximately 83 % of all Spanish inhabitants born in 1999 were enrolled in school during the data-collection period (2014/2015). Close to 100 % of the Spanish students born in 1999 were covered by the sampling frame.

A two-stage cluster sampling was used, by randomly selecting 941 schools in a first stage and 1 858 classes in a second stage. In order to select the schools, the sampling frame was first stratified by region (19 strata) and school type (public and private schools). Schools and classes had the same probability of being sampled, regardless of size. Data were weighted by region, type of school (public/private) and type of studies (secondary, high school and vocational education).

For comparison with the ESPAD study, data are reported only for the 18 280 students who were 15 or 16 years old at the time the survey was performed, with a mean age of 15.49.

Field procedure

All students in the sampled classes completed the questionnaire during a regular lesson (45-60 minutes). The anonymous character of the study was stressed by the survey leader prior to asking the students to complete the questionnaire. Teachers introduced the survey leaders (two per classroom) and were asked to remain in the classroom to ensure an orderly atmosphere. Teachers remained in the classroom and were asked not to walk around the room. Each student received an individual envelope in which to deposit the questionnaire once it was completed. Before leaving the classroom students were asked to give the envelope to the survey leader.

Data were collected from 14 November to 22 December 2014, and from 1 February to 8 April 2015. The survey was interrupted during the Christmas holidays and for a month thereafter to avoid bias in questions concerning the last-30- day period.

School and student participation

The information in this section refers to the whole sample (14 to 18-year-old students). The cooperation of the schools was excellent. The proportion of schools replaced because of a justified refusal to participate was 12.7 %.

About 15 % of registered students were not in class at the time of the survey (absent) for different reasons.

Student cooperation was very good. The proportion of students who declined to take part in the study was irrelevant (0.1 %).

Questionnaire and data processing

A standardised, anonymous questionnaire was used, which may be considered comparable with many questions used in the ESPAD questionnaire.

The questionnaire includes questions on sociodemographic characteristics, drug use, risk associated with different drug use behaviours, certain aspects related to entertainment, level of perceived availability of different psychoactive drugs, certain social and health-related problems, gathered information on drugs, drug use by friends and classmates, short cannabis abuse screening test (CAST), new psychoactive drugs (spice, ketamine, mephedrone, and salvia), students’ perception of their parents’ attitude regarding drug use and questions about the internet and gambling.

The linguistic particularities of the various autonomous regions were taken into account. Because of this, special versions of the questionnaire were used in the Basque, Castilian, Catalan, Galician and Valencian languages.

Data entry and the first checks for consistency were carried out by Análisis e Investigación, SL. Later on, a more detailed data check and analysis (selection of cases, recoding of variables, assignment of missing-data codes and data weighting) was carried out by the Spanish Observatory on Drugs and Drug Addiction. Due to missing information on age, gender or otherwise a high rate of non-responses, 1.5 % of all questionnaires were discarded.

Weightings were added to the data to improve the accuracy of estimates by correction for unequal probabilities of selection that arise in the multistage sampling procedures.

Reliability and validity

Results from the different surveys conducted since 1994 show tendencies that are rather consistent, suggesting that the data presented satisfy international standards of quality for school surveys. As mentioned, the reliability and validity seem to be high. It is assumed, however, that any remaining bias is in the direction of under-reporting.

It was found that self-reported drug use relates in consistent and expected ways to a number of attitudes, behaviours, beliefs and social situations; in other words, there is strong evidence of construct validity. The missing data rates for the self-reported-use questions are only slightly higher than for the preceding non-sensitive questions, in spite of the explicit instruction to respondents to leave blank those drug use questions they felt they could not answer honestly.

This is not to argue that self-reported measures of drug use are valid in all cases. The fieldworkers tried to create a situation and set of procedures in which students felt that their confidentiality was protected. They also tried to present a convincing case as to why such research is needed. Evidence suggests that a high level of validity has been obtained.

Methodological conclusions

The Spanish school surveys on drug use seem to have functioned well since their initiation in 1994. In 2014-2015 there are clearly trends of stabilisation in the prevalence rates of alcohol consumption (and also a decreasing trend in intoxication due to alcohol drinking) and significantly decreasing trends in the prevalence rates of cannabis, cocaine, tobacco, amphetamine, ecstasy and heroin consumption. There is a decrease in risk perception of occasional consumption and in perceived availability. These trends are consistent with those found in household surveys and in some of the drug-related indicators (drug-related deaths, drug-related infectious diseases, etc.).

The sample is representative of the whole country, and the number of students is large enough in relation to the 15- to 16-year-old cohort, which is the ESPAD target group. The level of cooperation shown by schools and students was very good.

There were 514 variables in the Spanish questionnaire, which is higher than in all ESPAD countries. However, since the average time to answer the questionnaire was within one lesson, it seems reasonable to assume that the length of the questionnaire has not negatively influenced the validity. About 0.1 % of the students did not participate, mostly because they simply refused to collaborate. The information provided by the survey leaders did not indicate any major problems, so there is reason to believe that student cooperation was good.