Quality of life in infants and children with atopic dermatitis: Addressing issues of differential item functioning acros
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Quality of life in infants and children with atopic dermatitis: Addressing issues of differential item functioning across countries in multinational clinical trials Stephen P McKenna*1,2, Lynda C Doward2, David M Meads2, Alan Tennant3, Gemma Lawton3 and Jens Grueger4 Address: 1Department of Psychology, University of Central Lancashire, Preston, UK, 2Galen Research, Manchester, UK, 3Academic Unit of Musculoskeletal & Rehabilitation Medicine, University of Leeds, Leeds, UK and 4Pricing and Health Economics, Novartis Pharma AG, Basel, Switzerland Email: Stephen P McKenna* - [email protected]; Lynda C Doward - [email protected]; David M Meads - [email protected]; Alan Tennant - [email protected]; Gemma Lawton - [email protected]; Jens Grueger - [email protected] * Corresponding author
Published: 27 July 2007 Health and Quality of Life Outcomes 2007, 5:45
doi:10.1186/1477-7525-5-45
Received: 14 March 2007 Accepted: 27 July 2007
This article is available from: http://www.hqlo.com/content/5/1/45 © 2007 McKenna et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract Background: A previous study had identified 45 items assessing the impact of atopic dermatitis (AD) on the whole family. From these it was intended to develop two separate scales, one assessing impact on carers and the other determining the effect on the child. Methods: The 45 items were included in three clinical trials designed to test the efficacy of a new topical treatment (pimecrolimus, Elidel cream 1%) in the treatment of AD in infants and children and in validation studies in the UK, US, Germany, France and the Netherlands. Rasch analyses were undertaken to determine whether an internationally valid, unidimensional scale could be developed that would inform on the direct impact of AD on the child. Results: Rasch analyses applied to the data from the trials indicated that the draft measure consisted of two scales, one assessing the QoL of the carer and the other (consisting of 12 items) measuring the impact of AD on the child. Three of the 12 potential items failed to fit the measurement model in Europe and five in the US. In addition, four items exhibiting differential item functioning (DIF) by country were identified. After removing the misfitting items and controlling for DIF it was possible to derive a scale; The Childhood Impact of Atopic Dermatitis (CIAD) with good item fit for each trial analysis. Analysis of the validation data from each of the different countries confirmed that the CIAD had adequate internal consistency, reproducibility and construct validity. The CIAD demonstrated the benefits of treatment with Elidel over placebo in the European trial. A similar (non-significant) trend was found for t
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