*2.3. Measures*

Four evaluation instruments were used to assess the variables in this study, under the psychometric parameters of reliability and validity.

The Kidscreen-10 Index [58] was used to assess subjective health-related quality of life and well-being. This 10-item scale was designed for children and adolescents aged 8–18 years. Each item has five response options, ranging from 'Never' to 'Always' or 'Not at all' to 'Extremely'. The 10 items cover: a ffective symptoms of depressed mood; cognitive symptoms of disturbed concentration; psychovegetative aspects of vitality, energy and feeling well; and psychosocial aspects correlated with mental health, such as the ability to experience fun with friends or getting along well with others at school. The adapted version of the questionnaire used in this study has adequate internal consistency reliability (*Cronbach's alpha* = 0.82) and test-retest stability (*r* = 0.73; *ICC* = 0.72) [59].

The Positive and Negative A ffect Schedule [60] was used to assess participants' positive and negative a ffect. The Spanish version of this scale for children and adolescents was validated by Sandín [61]. This scale comprises 20 items on two dimensions: positive a ffect and negative a ffect. Each subscale contains 10 items. The questionnaire is completed by participants based on the way they normally feel and behave. The scale has three response options: 'Never' = 1, 'Sometimes' = 2, and 'Many times' = 3.

We used the Trait Emotional Intelligence Questionnaire Adolescents Short Form (TEIQue-ASF) [62] (adapted into Spanish in its abridged version for teenagers by Ferrando and Serra [63]) to evaluate trait emotional intelligence based on the theoretical model of Petrides and Furnham [64]. The 30 items that make up the TEIQue-ASF are scored on a 7-point Likert scale (1 = 'Completely disagree' to 7 = 'Completely agree'). The general emotional intelligence score of the total scale is obtained by summing the 30 items.

Finally, participants completed the Social Anxiety Scale for Adolescents (SAS-A) [65]. The SAS-A comprises 22 items; 18 items are self-descriptive and four are distracting elements that are not taken into account for the score. The SAS-A contains three subscales: (a) fear of negative evaluation (eight items), (b) anxiety and social avoidance before strangers or new social situations (six items) and (c) anxiety and social avoidance in social situations in general (four items). Responses are on a 5-point Likert-type scale from 1 ('Never') to 5 ('Always'). In addition, a global index of social anxiety (SAS-T) is obtained by summing the scores for the items (excluding neutral items). High scores reflect high levels of social anxiety [65]. The scale was adapted to the Spanish population by Olivares, Ruiz, Hidalgo, García-López, Rosa and Piqueras [66]. Only the SAS-T score was used in this study.
