Refinement and reduction of the Impact of Psoriasis Questionnaire: classical test theory vs. Rasch analysis

The British Journal of Dermatology
T NijstenR S Stern

Abstract

Quality of life instruments are increasingly important in assessing disease severity. However, some of these measurements have been developed on a more or less ad hoc basis. Although not well standardized, psychometric analyses can be used to retest, refine and shorten existing quality of life instruments. To psychometrically test and refine the Impact of Psoriasis Questionnaire (IPSO) and to compare the results of two different statistical approaches. Among 792 psoriasis patients who were included in the PUVA Follow-up Study, we used classical test theory (CTT) and Rasch analysis to test and optimize the IPSO. Thereafter, two shortened versions of the IPSO derived from these models were compared. CTT analyses of the original IPSO demonstrated suboptimal item performance for six of 16 items and inappropriate subscaling. In contrast to the original four subscales, factor analysis of the CTT version yielded three subscales (mental functioning, mental wellbeing and stigmatization). The Rasch approach, which included ordering of thresholds, differential item functioning and item fit, resulted in a unidimensional 11-item questionnaire. Although the two new versions of the IPSO shared only six items, both reflected the original IPSO ...Continue Reading

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Citations

Oct 4, 2007·Dermatology : International Journal for Clinical and Investigative Dermatology·Tamar NijstenDamiano Abeni
May 26, 2012·Health and Quality of Life Outcomes·Esteban DaudenNuria Lara
Apr 1, 2006·The Journal of Investigative Dermatology·Jane UnaezeRobert S Stern
Jan 24, 2015·The Journal of Investigative Dermatology·Sarah L ChamlinAnita N Haggstrom
Mar 18, 2006·The Journal of Investigative Dermatology·Tamar E C NijstenDamiano D Abeni
Feb 14, 2015·The British Journal of Dermatology·H KitchenC Bundy
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Apr 29, 2015·Disability and Rehabilitation·Stephen AshfordRoxana Alexandrescu
Mar 15, 2011·Journal of the European Academy of Dermatology and Venereology : JEADV·A PicardiW H Rogers

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