DLQI and CDLQI scores should not be combined

Funding sources: none. Conflicts of interest: A.Y.F. is joint copyright owner of the DLQI and CDLQI. Cardiff University receives income from the use of these measures. Madam, There have been few attempts to assess the impact of interventions on quality of life in people with ichthyosis, so Bodemer et al.1 are to be congratulated on their interest in this area and on collecting Dermatology Life Quality Index (DLQI) data from 24 adults and Children’s Dermatology Life Quality Index (CDLQI) data from 20 children. Unfortunately, instead of presenting these data separately, they have combined the scores, thereby potentially invalidating the results as presented. They state ‘Both questionnaires can be calculated into one overall summary score’. This is not correct: they should not be combined in this way. The DLQI and CDLQI have different questions specific to the age groups for which the questionnaires are designed. It therefore would not be expected that the scoring characteristics would be the same. The validated score banding descriptors, for example, are different2, 3 and although there are data concerning the minimum clinically important difference for the DLQI,4 such data are not yet available for the CDLQI. The authors state correctly1 that ‘Both the DLQI and the CDLQI contain 10 questions relating to six headings’. However, both the heading descriptors and the number of questions under each heading are different. This information is available at http://www.dermatology.org.uk and our team is happy to give advice over such matters (dermqol@cf.ac.uk).