Background: Few weight-specific outcome measures, developed specifically for obese and overweight adolescents, exist and none are suitable for the elicitation of utility values used in the assessment of cost effectiveness.
Objectives: The development of a descriptive system for a new weight-specific measure.
Methods: Qualitative interviews were conducted with 31 treatment-seeking (above normal weight status) and non-treatment-seeking (school sample) adolescents aged 11-18 years, to identify a draft item pool and associated response options. 315 eligible consenting adolescents, aged 11-18 years, enrolled in weight management services and recruited via an online panel, completed two version of a long-list 29-item descriptive system (consisting of frequency and severity response scales). Psychometric assessments and Rasch analysis were applied to the draft 29-item instrument to identify a brief tool containing the best performing items and associated response options.
Results: Seven items were selected, for the final item set; all displayed internal consistency, moderate floor effects and the ability to discriminate between weight categories. The assessment of unidimensionality was supported (t test statistic of 0.024, less than the 0.05 threshold value).
Conclusions: The Weight-specific Adolescent Instrument for Economic-evaluation focuses on aspects of life affected by weight that are important to adolescents. It has the potential for adding key information to the assessment of weight management interventions aimed at the younger population.
Keywords: Adolescents; Condition-specific measure; Economic evaluation; Instrument development; Instrument refinement; Obesity; Quality of life; Rasch analysis.