2.2. Instruments

Gambling frequency. The question on the ESTUDES survey was used. It contains two items (online and in person) that evaluate gambling frequency (number of times) on a 5-point Likert scale (never having gambled, not having gambled in the past 12 months, gambled monthly, weekly, or daily).

Type of game in which they have bet money. The analysis was performed by using an adaptation of the 14-question instrument from the ESTUDES survey, which evaluates different types of gambling. For the two items (online and in person), the participant is asked to indicate the types of gambling in which they have participated in the past 12 months. The 12 options (multiple choice) are Lotteries, Instant lotteries, Football pools, Sport bets, Horse racing bets, Slots and slot machines, Cash games and cards, Bingo, Video games, eSports or electronic sports, Casino games, and Games in gambling halls.

Gambling intensity. An adaptation of items from the ESTUDES survey was also used. For the two items (online and in person), the questionnaire includes 5 of the 7 questions from the original questionnaire to evaluate the participants who had gambled money in the past 12 months. The five questions are associated with five categories of intensity, corresponding to different maximum amounts of money gambled in a day. The response options were: less than €6, between €6 and €30, between €31 and €60, between €61 and €300, more than €300, I have not bet money in the past 12 months, and I have never bet money.

Strengths and Difficulties Questionnaire (SDQ) [21]. The SDQ is a widely-used measurement instrument to assess behavioral and emotional difficulties and social skills. In addition, this questionnaire is commonly used as a tool for psychopathological screening and epidemiological analysis of the state of mental health in the youth population. The SDQ, through a brief, simple, and easy to administer questionnaire, makes it possible to obtain reliable samples of conducts related to emotional and behavioral problems (Fonseca, 2017). It is composed of 25 items with a 3-point Likert scale (0 = no, never, 1 = sometimes, 2 = yes, always). The items are grouped in five scales with five items each: Emotional Difficulties; Conduct Problems; Hyperactivity Difficulties; Problems with Peers; and Prosocial Behavior. The first four scales make up the Total Difficulties score. The higher the score, the higher the level of emotional and behavioral difficulties. In contrast, in the case of the Prosocial Behavior scale, a lower score is associated with worse behavioral adjustment [22]. In this study, we used the Spanish version of the scale [23]. The level of internal consistency of the Total difficulties score was 0.84, ranging between 0.71 and 0.75 for the SDQ subscales.

Rosenberg Self-esteem Scale [24]. It is a unidimensional scale that makes it possible to assess self-esteem. Its 10 items are statements that can be used to assess self-esteem (e.g., I think I have reasons to feel proud). The items have a 4-point Likert scale (from 1 = strongly disagree to 4 = strongly agree). The scale showed good reliability in this sample (α = 0.87).

Reynolds Adolescent Depression Scale Short Form (RADS-SF) [25]. This instrument, through its 10 items, evaluates the severity of depressive symptomatology in adolescence. The items cover different dimensions (Anhedonia, Somatic complaints, Negative self-evaluation. and Dysphoria), and responses are given on a 4-point Likert scale (from 1 = almost never to 4 = almost always). It is a widely used scale, validated by studies such as the one by Ortuño-Sierra et al. [26].

Personal Wellbeing Index-School Children (PWI-SC) [27,28]. The PWI-SC is an instrument used to assess subjective wellbeing in school-aged children and adolescents (PWI-SC). It is composed of eight items that measure, in a generic and abstract way, subjective satisfaction with a specific life domain. The items have several response options, ranging from very dissatisfied (score of 0) to very satisfied (score of 10). The first item analyzes "life as a whole", whereas the other seven items refer to satisfaction with: health; standard of living; accomplishments in life; how secure they feel; the groups of people they are part of; future security; and their relationships with other people. The overall score is obtained by adding up the scores on the seven items (except item one). The PWI-SC has been validated in previous studies with adolescents, both nationally and internationally [22]. The scale showed good reliability in this sample (α = 0.94).