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