Validation of the questionnaire Skindex-17

Skin diseases have a significant impact on the health-related quality of life
(HRQOL) of patients. It is believed that the impact of inflammatory
skindiseases such as psoriasis and atopic dermatitis are comparible to the
effect of other chronic diseases such as diabetes, reumatic artritis,
hypertension and Crohn*s disease. To measure the impact of diseases on the
quality of life, several instruments are available and these can be grouped in
generic instruments (eg. SF-36), dermatology-specific instruments (eg.
Skindex-29 and Dermatology Life Quality Index: DLQI) or disease-specific
questionnaires (eg. Psoriasis Disability Index). The majority of the
dermatology-specific instruments have been developed in the early 90*s, of
which the Skindex-29 among the most commonly used and widely accepted tools.
Recently we have reduced the Skindex-29 using item response theory models in
the Skindex-17. The later is fitted both the classical test theory and item
response theory model well in a population of Italian dermatology patients.
However, before new instruments are accepted, they should be validated
extensively in populations that vary culturally, demographically and in
diseases severity.

Little is known what drives patients to score HRQOL items or global
assessments. Although it has not been studied previously, it is likely that
several demographic and disease related factors are important predictors of how
patient rate their disease and the impact of their disease on their lives. The
only varieble studied is clinical disease severity (assessed by the
dermatologists) and, surprisingly, several studies show that the level of
clinical disease severity is not well correlated with HRQOL impairment.
Identifying these predictors may help us to better understand outcome
measurements used in dermatology.
Moreover, dermatologists underestimate the impact of the disease on patients`
lifes substantially. This may affect the management patients need or expect,
which may result in dissatisfied patients. To maximize patinets`treatments it
would be usefull to study and potential predictors of the discrepancy between
patients and physicians assessments. In reumatology, it has been demonstrated
that there are significant differences between the patinet and physician global
assessmnets. Factors significantly associated factors with this discrepancy
were eg. age, descent and education level of the patient.

The goal of this study is to validate and interpret a new HRQOL instrument and
to analyse commonly used outcome measurements (PGA, PtGA) in dermatology.

A cross sectional study of patients visiting the outpatient clinic of the
Department of Dermatology. At most at three monents in time, patinets are asked
to complete a questionnaire.

Time strain: Filling in questionnaires
First visit: 30 minutes
48 h after first visit (just new patients): 5 minutes
First control visit: 5 minutes