Published online by Cambridge University Press: 18 August 2016
Defining minimal important difference (MID) is critical to interpreting patient-reported outcomes data and treatment efficacy in clinical trials. This study estimates the MID for the Weiss Functional Impairment Rating Scale–Parent Report (WFIRS-P) and the Child Health and Illness Profile–Parent Report (CHIP-CE-PRF76) among parents of young people with attention-deficit/hyperactivity disorder (ADHD) in the UK.
Parents of children (6–12 years; n=100) and adolescents (13–17 years; n=117) with ADHD completed a socio-demographic form, the CHIP-CE-PRF76, the WFIRS-P, and the Pediatric Quality of Life scale at baseline and 4 weeks later. At follow-up, a subset of parents completed anchor questions measuring change in the child/adolescent from baseline. MIDs were estimated using anchor-based and distribution-based methods, and separately for children and adolescents.
The MID estimates for overall change in the WFIRS-P total score ranged from 11.31 (standard error of measurement) to 13.47 (anchor) for the total sample. The range of MID estimates for the CHIP-CE-PRF76 varied by domain: 6.80–7.41 (satisfaction), 6.18–7.34 (comfort), 5.60–6.72 (resilience), 6.06–7.57 (risk avoidance), and 4.00–5.63 (achievement) for the total sample. Overall, MID estimates for WFIRS-P MID and CHIP-CE-PRF76 were slightly higher for adolescents than for children.
This study estimated MIDs for these instruments using several methods. The observed convergence of the MID estimates increases confidence in their reliability and could assist clinicians and decision makers in deriving meaningful interpretations of observed changes in the WFIRS-P and CHIP-CE in clinical trials and practice.
Affiliation at the time of the study.
This research was funded by Shire Development LLC. The authors would like to acknowledge input by Sarah Hearn (University of Oxford, Oxford, UK) for assistance with the statistical analysis of the study. Editorial assistance in formatting, proofreading, copyediting, and coordination and collation of comments for the manuscript was provided by Caudex (funded by Shire International GmbH, Switzerland). Although employees of Shire were involved in the design, collection, analysis, interpretation, and fact checking of information, the content of this manuscript, the ultimate interpretation, and the decision to submit it for publication in CNS Spectrums was made by the authors independently. The authors are entirely responsible for the scientific content of the paper.
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