The weight-specific adolescent instrument for economic evaluation (WAItE): psychometric evaluation using a Rasch model approach
The Weight-specific Adolescent Instrument for Economic evaluation (WAItE) is a 7-item condition-specific tool assessing the impact of weight status on seven dimensions of quality of life. The content of the WAItE was developed with both treatment-seeking and non-treatment-seeking adolescents aged 11–18 years. The aim of this study was to assess the psychometric properties of the WAItE in adolescent and adult populations.
Treatment-seeking adolescents with obesity (females n = 155; males n = 123; mean age = 13.3; 13.1 years, respectively) completed the WAItE twice. An adult general population sample completed the WAItE via an online survey (females n = 236; males n = 231; mean age = 41.2; 44.3 years, respectively). The Partial Credit Model was applied to the data and item fit evaluated against published criteria.
The WAItE had a unidimensional structure both for adolescents and adults. There was no item misfit observed for either participant samples and no differential item functioning (DIF) was present by age or gender for the adolescents. Some DIF was observed across age groups for the adult sample. For the adolescent sample, stable item locations were observed over time.
The aim of the WAItE is to assess the impact of weight status on the lives of adolescents in cost-effectiveness evaluation of weight management programmes. The results of this study demonstrated that the WAItE has reliable psychometric properties. The instrument may therefore be used to aid informed decision around the identification of cost-effective weight management programmes in both adolescent and adult populations.
KeywordsObesity Quality of life Economic evaluation Adolescents Condition-specific measure Rasch analysis Adults
We would like to acknowledge the advice and support of the following individuals: Cathy Brennan, Jenny Hewison, Donna Lamping, Christopher McCabe, David Meads, Jennifer Roberts, Katherine Stevens, Alan Tennant. We would like to acknowledge Aki Tsuchiya (PhD supervisor) for her guidance and support throughout the fellowship project. Finally, we would like to thank all the participants who took part in the research and the parents and staff who supported this research.
The work presented here was part of a National Institute for Health Research (NIHR) funded fellowship project awarded to the first author (DFR/2009/02/101). This paper presents independent research funded by the National Institute for Health Research (NIHR). The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Ethical approval was provided by the University of Leeds, School of Medicine Research Ethics Committee for both the adolescents and adult studies (Ref: HSLTLM/11/049).
Both of the weight management services followed their own procedures for obtaining consent. All parents and carers of adolescents provided written or oral consent for adolescents to complete the WAItE. If parents did not object, then written or oral assent (under 16 years)/consent (16 years plus) for all participating adolescents was obtained. Anonymised datasets were provided directly from weight management organisations who adhered to strict security protocols. Adult participants who were recruited from a consumer panel provided consent to the market research company to be approached and complete web surveys.
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