2.1. Sample and Study Design

We analyzed data from a cross-sectional survey conducted in a representative sample of non-institutionalized adults in Spain as part of the MIND/COVID project [34]. The target population of the survey included people who were both aged 18 years or older and had no language barriers. Computer-assisted interviews (CATI) were carried out by a bureau of professional interviewers during June 2020. The sample was drawn through a dual-frame random digit dialing (RDD) telephone survey, and it included both landlines and mobile telephones. The distribution of the interviews was planned according to quotas proportional to the Spanish population in terms of age groups, sex, and the region of residence [35].

A total of 138,656 numbers were sampled, with a final split of 71% mobile telephones and 29% landline telephones. Of them, 45,002 were classified as non-eligible (i.e., 43,120 had non-existing numbers, 984 were numbers of enterprises, 444 were numbers of persons with Spanish language barriers, 268 were fax numbers, 186 numbers belonged to the quota that was already completed), and 72,428 had unknown eligibility (i.e., no contact was made after the seven attempted calls), resulting in a 19.7% cooperation rate (i.e., the proportion of all cases interviewed of all eligible units ever contacted). Finally, 3500 people were interviewed during the COVID-19 lockdown in Spain, from which only 2381 belonged to the active population (see Figure 1). Interviews included general demographic questions and questions related to social networks and living situations, socioeconomic factors, the use of health resources, mental health, general health, and wellbeing. For mental health, depression, anxiety, PTSD symptoms, panic attacks, substance abuse, and suicidal thoughts and behaviors were asked by means of validated questionnaires. Ethical approval was provided by Fundació Sant Joan de Déu, Barcelona, Spain (PIC 86−20) and by the Parc de Salut Mar Clinical Research Ethics Committee (protocol 2020/9203/I). Oral consent was obtained once the selected participant was fully informed about the objectives and procedures of the study to proceed with the interview.

Flow-chart of the study sample.