Construct validity and responsiveness of Skindex‐29‐Colombia

Abstract

Until three decades ago, the understanding of disease and treatment effects on patients’ daily lives was very poor. More recently, and due to the fact that international scientific collaboration has increased, patient-reported outcomes (PRO) and quality-of-life (QOL) in particular, have become essential tools to evaluate the effect of any medication according to the patient´s perspective. However, as most QOL scales have been developed in English, there is a growing need to adapt them for use across different cultures but to make sure that the original instrument (scale) and the adapted scale are equivalent, a process that has been called “validation”. As QOL is a complex concept in which the precise meaning of questions can vary between individuals of different countries and cultures, so establishing its validity is quite difficult. In this respect, construct validity (instrument ability to measure a construct or concept), convergent/discriminant validity (correlation/lack of correlation of the instrument in comparison to another instrument), and responsiveness (instrument ability to detect change over time) are all crucial properties that test the instrument's accuracy. Therefore, this study aimed to assess these properties in the Colombian version of Skindex-29, which is a QOL scale. Validity and responsiveness were tested in 209 dermatology patients and 56 people without skin disease. Patients had either inflammatory or non-inflammatory skin diseases. Construct validity was assessed through a test called confirmatory factor analysis, which shows the relationship between all questions (items) of the instrument, and how they cluster around the QOL concept. The convergent/discriminant validity was evaluated by a test called the Spearman correlation coefficient, and responsiveness was tested through the standardized response mean. The authors found that the Colombian version of Skindex-29 is a valid and clinically sensitive instrument that can be used for clinical practice (e.g. by doctors treating patients) and for research, to measure the impact of skin diseases on quality-of-life in dermatology patients.