Comments on ‘Validity and responsiveness of the Osnabru ¨ck Hand Eczema Severity Index (OHSI): a methodological study’ DOI: 10.1111/j.1365-2133.2009.09262.x SIR, We have read with interest the paper by Dulon et al. which was published in the January 2009 issue of the Journal. 1 Assessing severity of hand dermatitis is essential if one endeavours to assess the burden of disease accurately in clini- cal settings and epidemiological research from an objective point of view. Several attempts have been made in this respect, including the development of a photographic guide 2 and two different types of hand dermatitis severity indices which have both been evaluated for reliability. 3,4 Going beyond reliability assessment, Dulon and coworkers provide a valuable and important study on the validity and ‘responsiveness’ for one of these – the Osnabru ¨ck Hand Eczema Severity Index (OHSI). 1 Their aim is twofold: (i) to assess convergent and discriminant validity; and (ii) to assess longitudinal construct validity (‘responsiveness to change’). We believe that these two aims were compromised by two related errors. Firstly, evidence for convergent and discrimi- nant validity is derived by comparing the OHSI with another measure of hand eczema severity, the Manuscore, which is considered a ‘gold standard’ for the purposes of this study. Spearman correlation coefficients and limits of agree- ment are computed to assess convergent validity with this standard, and discriminant validity is assessed as the sensiti- vity, specificity, positive and negative predictive value against this standard. The adopted ‘gold standard’ criterion is prob- lematic, however, which is acknowledged by Dulon et al. in the discussion section: ‘A potential source of bias may be that (…) no data on validity have been assessed for the Manuscore’. They justify the choice of the Manuscore as the gold standard because it is a very precise documentation of severity of hand dermatitis and because it was developed to comply with quality standards for sociolegal evaluation in occupational dermatology in Germany. The Manuscore might be precise, it might even possess face and content validity and yet not be valid in the full sense of the term ‘validity’, i.e. the degree to which an instrument measures what it purports to measure. 5 We simply do not know until data on construct validity are published. Besides, the only refer- ence which is currently given relates to a book chapter, and not a peer-reviewed paper. 6 It has been noted in other fields of inquiry that claiming construct validity is easy, as the reverse is difficult to demonstrate. 7 However, comparing a new measure (OHSI) against a measure without published data on validity (Manuscore) is in itself not valid. It would have been a much better option to evaluate the OHSI against the Hand Eczema Severity Index 3 or the photo- graphic guide. 2 The second error also relates to an unvalidated criterion. Dulon et al. assume that treatment was ‘generally successful’ and conclude from calculated effect sizes that the OHSI is able to detect change and hence is suitable for monitoring purposes. If there were a treatment effect, then calculating an effect size using the OHSI would yield evidence for ‘responsiveness’. But if the presence of a treatment effect is determined by a change in OHSI scores, this cannot validate the OHSI: this would be to argue that there was a treatment effect because the OHSI scores changed, and that the OHSI was valid because it registered the treatment effect. ‘Respon- siveness’ cannot be established if the effect size is uncorrob- orated (this is a common error in the literature). Rigorous validation studies are mandatory from a methodological point of view, but should also be conducted for the ulti- mate benefit to patients in the context of evidence-based medicine. C.J. A PFELBACHER M. H ANKINS * Department of Clinical Social Medicine, University Hospital Heidelberg, 69115 Heidelberg, Germany *Division of Primary Care and Public Health, Brighton and Sussex Medical School, Mayfield House, University of Brighton, Falmer BN1 9PH, U.K. E-mail: christian.apfelbacher@med.uni-heidelberg.de References 1 Dulon M, Skudlik C, Nu ¨bling M et al. Validity and responsiveness of the Osnabru ¨ck Hand Eczema Severity Index (OHSI): a methodologi- cal study. Br J Dermatol 2009; 160:137–42. 2 Coenraads PJ, van der Walle H, Thestrup-Pedersen K et al. Construction and validation of a photographic guide for assessing severity of chronic hand dermatitis. Br J Dermatol 2005; 152:296– 301. 3 Held E, Skoet R, Johansen JD, Agner T. The Hand Eczema Severity Index (HECSI): a scoring system for clinical assessment of hand eczema. A study of inter- and intraobserver reliability. Br J Dermatol 2005; 152:302–7. 4 Skudlik C, Dulon M, Pohrt U et al. Osnabrueck hand eczema severity index – a study of the interobserver reliability of a scor- ing system assessing skin diseases of the hands. Contact Dermatitis 2006; 55:42–7. 5 Assessing health status and quality-of-life instruments: attributes and review criteria. Qual Life Res 2002; 11:193–205. 6 John SM. Diagnostics in the investigation of occupational skin diseases – I. Operationalisation of the clinical findings (Manuscore). In: Clinical and Experimental Studies of Diagnostics in Occupational Dermatology (John SM, ed.). Osnabru ¨ck: Universita ¨tsverlag Rasch, 2001; 133– 41. 7 Hyland ME. Quality-of-life assessment in respiratory disease: an examination of the content and validity of four questionnaires. Pharmacoeconomics 1992; 2:43–53. Key words: responsiveness, validity Conflicts of interest: none declared. Ó 2009 The Authors Journal Compilation Ó 2009 British Association of Dermatologists • British Journal of Dermatology 2009 161, pp470–492 Correspondence 481