INVESTIGATIVE REPORT
59 Advances in dermatology and venereology ActaDV Acta Dermato-Venereologica ActaDV
Rasch Analysis of the Dermatology Life Quality Index Reveals Limited Application to Chinese Patients with Skin Disease
Zehui HE 1 #, Riccardo LO MARTIRE 2, 3 #, Chuanjian LU 4, 5, Hongxia LIU 6, Lin MA 7, Ying HUANG 8, Yongmei LI 9, Liyun SUN 10, Yanping BAI 11, Wali LIU 12 and Xushan ZHA 13
1
Department of Clinical Epidemiology, 4 Department of Dermatology, Guangzhou University of Chinese Medicine Second Affiliated Hospital, Guangzhou, China, 2 Department of Aeronautical and Vehicle Engineering, KTH Royal Institute of Technology, 3 Department of Neurobiology, Care Sciences and Society, Karolinska Institutet, Stockholm, Sweden, 5 Key Laboratory of Clinical Research on Traditional Chinese Medicine Syndrome, Guangdong Provincial Academy of Chinese Medical Sciences, Guangzhou, Departments of Dermatology, 6 Xinjiang Medical University Affiliated Chinese Medicine Hospital, Urumqi, 7 Heilongjiang Provincial Academy of Chinese Medical Sciences, Harbin, 8 Chengdu University of Traditional Chinese Medicine Affiliated Hospital, Chengdu, 9 Shanghai University of Traditional Chinese Medicine Affiliated Longhua Hospital, Shanghai, 10 Capital Medical University Affiliated Beijing Traditional Chinese Medicine Hospital, Beijing, 11 China-Japan Friendship Hospital,
12
China Academy of Chinese Medical Sciences Guanganmen Hospital, Beijing, and 13 Guangzhou University of Chinese Medicine First Affiliated Hospital, Guangzhou, China
#
These authors contributed equally to this work.
The objective of this study was to examine the psychometric properties of the Chinese version of the Dermatology Life Quality Index( DLQI) and to assess the invariance of its items with respect to several patient parameters via Rasch analysis. Data were aggregated from 9,845 patients with various skin diseases across 9 hospitals in different regions of China. The response structure, local independence, and reliability of the DLQI scale were analysed in a partial credit model, and differential item functioning( DIF) across region, disease, sex, and age were assessed with a Mantel- Haenszel procedure. Although acceptable scale reliability( Person Separation Index = 2.3) was obtained, several problems were revealed, including disordered response thresholds, misfitting items, DIF by geographical region and disease, and mis-targeting patients with mild impairment regarding health-related quality of life( HRQL). In conclusion, the DLQI provides inadequate information on patients’ impairments in HRQL, and the application of the DLQI in Chinese patients with skin disease is limited.
Key words: Dermatology Life Quality Index; skin disease; Chinese; Rasch analysis; differential item functioning.
Accepted Jul 5, 2017; Epub ahead of print Jul 5, 2017 Acta Derm Venereol 2018; 98: 59 – 64.
Corr: Chuanjian Lu, Department of Dermatology, Guangzhou University of Chinese Medicine Second Affiliated Hospital, 111 Da De Road, Guangzhou 510120, China. E-mail: luchuanjian888 @ vip. sina. com
The Dermatology Life Quality Index( DLQI)( 1) has been translated into more than 90 languages and applied to over 40 different skin conditions( 2). It is the most commonly used health-related quality of life( HRQL) instrument in dermatology worldwide( 3, 4). The psychometric properties of the DLQI have been a controversial issue, due to contradictory results of studies using either classical or modern test theory approaches. Although acceptable psychometric properties have been reported for various DLQI translations when assessed via classical test theory approaches( 5 – 10), investigations based on Rasch analysis have identified several problems with the scale, including the Chinese version( 11 – 13).
Since the translation of the DLQI into Chinese in 2004( 10), 3 peer-reviewed studies focusing on its psychometric properties have been published: 2 were classical theory-based( 5, 10), and one was Rasch-based with a relatively small sample size of 150 patients with neurodermatitis( 13). The psychometric properties of the DLQI have not been evaluated adequately in a large sample of patients with skin disease, nor have its item response functions for 2 or more subgroups of skin diseases. Therefore, this study examined the response category structure, fitness of items and persons, and local independence of items of the Chinese version of the DLQI via Rasch analysis, and assessed the invariance of items with respect to several patient subgroups in 9,845 Chinese dermatology patients.
METHODS Design and participants
In this cross-sectional study, 9,845 dermatology patients were consecutively recruited in 9 hospitals from different geographical regions of mainland China between 2013 and 2015. Inclusion criteria were: minimum age 16 years, diagnosed skin disease, and ability to understand and read Chinese. Exclusion criteria were: mental or physical incapacity resulting in inability to complete the survey. This study was approved by the ethics committee of the Guangzhou University of Chinese Medicine Second Affiliated Hospital and conformed to the principles of the Declaration of Helsinki.
Initially, patients received information about the study and signed informed consent forms. Then they provided their demographic information and self-completed the DLQI. Dermatologists confirmed the skin disease diagnoses and assessed their severity on a 5-point Likert-type response from“ very mild” to“ very severe”.
Dermatology Life Quality Index
The DLQI is a self-administered questionnaire used to assess the impact of skin disease on HRQL. It contains 10 items covering 6 aspects of quality of life: symptoms and feelings, daily activities, leisure, work and school, personal relationships and problems
This is an open access article under the CC BY-NC license. www. medicaljournals. se / acta Journal Compilation © 2018 Acta Dermato-Venereologica. doi: 10.2340 / 00015555-2742 Acta Derm Venereol 2018; 98: 59 – 64