Heath-related quality of life was assessed using PedsQL™, a
reliable and valid questionnaire for children and adolescents
with chronic diseases [32–34]. PedsQL™ consists of four
subscales that evaluate generic aspects of health-related
quality of life. The raw values were transformed according
to the procedure of Varni et al. [34], with values
ranging from 0 to 100. Cronbach’s alpha reached values
between α 0 0.68 and α 0 0.80.
Pain-related cognitions were measured using a selfadministered
questionnaire based on the Itch-questionnaire
[36], which was adapted accordingly to match abdominal
pain. This questionnaire was already tested successfully in
our pilot study. It assesses positive cognitions (e.g., “When I
have abdominal pain, then I tell myself to stay calm and
relax”) and negative cognitions (e.g., “…the pain makes me
crazy”). Children rated the frequency of such cognitions on
a 6-point Likert scale (from 1 0 never to 6 0 always). In the
present set of data, Cronbach’s alpha reached 0.71 (positive
cognitions) and 0.69 (negative cognitions).