Abstract
BackgroundA 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.MethodsThe 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.ResultsRasch 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 the US trials.ConclusionThe study represents a novel method of dealing with the problem of DIF associated with different cultures. Such problems are likely to arise in any multinational study involving patient-reported outcome measures, as items in the scales are likely to be valued differently in different cultures. However, where all items in a scale fit both a single theoretical construct and the Rasch measurement model, it is feasible to conceive of outcome measures with a different set of items in each language.
Highlights
A previous study had identified 45 items assessing the impact of atopic dermatitis (AD) on the whole family
Forty-five potential items were identified covering issues of relevance to the affected child and to his or her siblings and parents. This item set was included in three clinical trials designed to test the efficacy of a new topical treatment for AD in the treatment of AD in children
Identification of the Childhood Impact of Atopic Dermatitis (CIAD) for the European trial Working with the 12 items that were specific to the child, the scale was initially analyzed separately for the four countries (France, Germany, The Netherlands and the UK)
Summary
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. Forty-five potential items were identified covering issues of relevance to the affected child and to his or her siblings and parents This item set was included in three clinical trials (two in the US and one in Europe) designed to test the efficacy of a new topical treatment for AD (pimecrolimus, Elidel® 1% cream) in the treatment of AD in children
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