*2.6. Self-Concept*

The FSK-K ("Fragebogen zur Erfassung von Selbst—und Kompetenzeinschätzungen bei Kindern") is a German version of Harter's Self-Perception Profile for Children [35] and has been used in previous studies in the context of childhood obesity [36]. It is a 30-item self-report to assess the multidimensional self-concept of children. Each item is scored on a scale of 1–4 in an alternative-statement format, with a positive statement on one side (e.g., "I want to stay the way I am") and a negative statement on the other side (e.g., "I would like to be someone else"). The child decided which side of the description was "sort of true" or "really true" for him/her.

The FSK-K integrates five scales for assessing perceived domain-specific self-concept: scholastic competence, social competence, physical appearance, behavioral conduct, and global self-worth. After recoding, the highest domain-specific competence was defined as a mean score of 100. Internal consistency of the domains of self-concept was α = 0.79 for scholastic competence (*n* = 231), α = 0.82 for social competence (*n* = 223), α = 0.76 for physical appearance (*n* = 215), α = 0.77 for behavioral conduct (*n* = 228), and α = 0.71 for global self-worth (*n* = 215).
