2.2. Measures

Eating disorders were measured using the Sick Control on Fast Food (SCOFF) questionnaire, a 5-item screening tool for identifying potential eating disorder pathology. The questionnaire has been validated in previous research on adolescent populations and showed good sensitivity and specificity [37,38,39]. Adolescents were asked if they ever make themselves sick because they feel uncomfortably full, if they worry they have lost control over how much they eat, if they recently lost more than 6 kg in a 3-month period, if they believe themselves to be fat when others say they are too thin, and if they would say that food dominates their life with yes/no response categories. The item “weight loss” was reformulated as original weight unit “stone” is not used in Slovak language. Thus, we defined this term as loss of more than 6 kg in 3 months. Responses were dichotomised into 2 groups: (1) adolescents with no or 1 symptom, and (2) adolescents with 2 or more symptoms [40].

Health literacy was measured by a brief 10-item Health Literacy for School-Aged Children (HLSAC) instrument. HLSAC was internationally validated for 13- and 15-year-olds [41] and was developed for the broader international use to measure general and subjective health literacy among school-aged children. HLSAC is constituted from 5 core components: theoretical (health) knowledge, practical (health) knowledge, critical thinking, self-awareness, and citizenship [35], and includes 2 items for each core component. All the items took the form “I am confident that . . .”, and the response options were (1) not at all true, (2) not quite true, (3) somewhat true, and (4) absolutely true. A sum-score was generated the responses to the 10 items with the range in total 10–40. The levels of health literacy were classified into 3 categories: “low” (score 10–25), “moderate” (score 26–35), and “high” (score 36–40).

Body image was assessed using responses to a question about how they perceived their body: “much too thin”, “a bit too thin”, “about right”, “a bit too fat”, or “much too fat”. In accordance with the HBSC international coding guidelines [42], we collapsed the responses into “perceived fat” (being a bit or much too fat), compared with “perceived not fat” (the other three options).