The participants in the baseline are men and women of legal age from all regions of Spain, residing in their private homes and who agreed to participate in the study. They were part of a national representative sample of the Spanish adult population, created using a multistage stratified probability method. Three subsamples were established according to age groups: 18 to 49 years; 50 to 79 years; and ≥80 years. The 50+ and 80+ year subgroups were oversampled, as they are the main objective of the study.
The survey protocol was translated from English to Spanish following the WHO translation guidelines for assessment tools (WHO, 2014). Professional interviewers were trained to do the survey prior to its administration. Strategies were implemented to ensure quality in data collection (Üstun et al, 2005).
The final response rate was 69.9%, corresponding to 4,583 adults over 18 years of age. Structured face-to-face interviews were conducted through personal computer or tablet-assisted interviews at the respondents’ homes.
Üstun TB, Chatterji S, Mechbal A, Murray CJL, WHS collaborating groups (2005) Chapter X: Quality assurance in surveys: standards, guidelines and procedures. In: United Nations, editor. Household Sample Surveys in Developing and Transition Countries. New York: United Nations Publications. p. 199–230.
World Health Organization (2014) WHO | Process of translation and adaptation of instruments. WHO website. https://www.who.int/substance_abuse/research_tools/translation/en/.