SlideShare a Scribd company logo
1 of 24
Rasch analysis of the Dermatology Life 
Quality Questionnaire (DLQI) 
James Twiss and Stephen McKenna 
Galen Research Ltd, Manchester, UK 
Email: jtwiss@galen-research.com
Objectives 
• To discuss good scale development 
methodology in the context of Rasch analysis 
• Example - Dermatology Life Quality Index 
(DLQI)
The DLQI 
• 10-item generic dermatology Patient Reported 
Outcome (PRO) measure 
• Scored 0-30. High scores=worse 
• Used with 30 different skin conditions 
• Available in 55 languages 
• Used for treatment selection in the UK
DLQI development 
• Uses patient reports of problems 
• 49 identified ‘aspects’ condensed into 10 items 
• Designed to fit on one side of A4 
• Items phrased to include additional aspects
The DLQI - content 
Sample DLQI items: Over the last week… 
how embarrassed or self conscious have you been because of 
your skin? 
how much has your skin interfered with you going shopping or 
looking after your home or garden? 
how much has your skin made it difficult for you to do any sport? 
how much of a problem has the treatment for your skin been, for 
example by making your home messy, or by taking up time?
The DLQI – response format 
• Four point response format 
– Very much 
– A lot 
– A little 
– Not at all 
• 8 items also have a ‘Not relevant’ option
Psychometric properties 
• Classical psychometric properties adequate 
(Basra et al, 2008) 
• One previous Rasch analysis compared 6 
language versions (Nijsten and Meads, 2007) 
– Overall misfit to the model 
– Misfit in 3 individual countries 
– DIF by country for every item
Study aims 
• Rasch analysis of DLQI data from two patient 
groups: 
- atopic dermatitis 
- psoriasis 
• Relate results to development methods used for 
DLQI
Analyses 
Rasch analysis employed RUMM2020 
• Overall fit to model 
• Individual Item fit 
• Response threshold order 
• DIF by age and gender 
• DIF by disease (AD vs psoriasis) 
• Item-trait coverage
Sample 
Psoriasis 
(n = 146) 
Atopic Dermatitis 
(n = 146) 
Gender (%) 
Male 73 (50) 73 (50) 
Female 73 (50) 73 (50) 
Age (Years) 
Mean (SD) 44.4 (14.7) 45.5 (16.6) 
Range 66 (17-83) 62 (20-82) 
Duration (years) 
Mean (SD) 20.9 (13.5) 28.2 (17.5) 
Range 67 (2-69) 76 (0-76)
DLQI scores 
Psoriasis Atopic dermatitis 
Mean (SD) 8.8 (6.7) 6.1 (4.6) 
Median (IQR) 7 (3.0-12.3) 5 (3-8) 
Range 29 (0-29) 26 (0-26)
Overall fit to the Rasch model 
Initial fit statistics (partial credit model) 
Item-trait 
interaction 
PSI 
Items Persons 
Mean SD Mean SD 
0.85 0.98 -0.30 0.81 
0.01 -0.81
Item fit 
Item description Location 
Fit 
residual Chi2 p value 
1. itchy, sore, painful or stinging -1.61 -0.03 3.4 0.50 
2. embarrassment/self consciousness -0.52 -1.97 15.0 
3. interferes with shopping/looking 
after home/garden 
0.005* 
0.99 -1.18 3.8 0.44 
4. influences choice of clothes -0.54 -0.14 4.4 0.35 
5. affects social/leisure activities 0.32 12.7 
6. affect ability to do sport -0.02 0.29 3.0 0.56 
7. prevents working/studying 0.25 0.23 12.6 
8. creates problems with partner/close 
friends/relatives 
-2.69 0.01 
0.01 
0.59 -0.89 2.1 0.72 
9. causes sexual difficulties 0.89 -1.23 2.2 0.70 
10. problems with treatment -0.36 -0.47 3.5 0.48
Problems with items 
• 2 - Over the last week, how embarrassed or self 
conscious have you been because of your skin? 
• 5 - Over the past week, how much has your skin 
affected any social or leisure activities? 
• 7 - Over the past week, how much has your skin 
prevented you working / studying?
DIF analysis 
Item description Uniform DIF 
Non-uniform 
DIF 
itchy, sore, painful or stinging Disease 
embarrassment/self consciousness Age group/Gender 
interferes with shopping/looking after 
home/garden 
Disease Disease 
influences choice of clothes Gender*/ Disease 
affects social/leisure activities Disease 
affect ability to do sport Gender Gender 
prevents working/studying Gender/Disease* 
creates problems with partner/close 
friends/relatives 
causes sexual difficulties 
problems with treatment Age group*
Example of DIF by disease 
Prevents working or studying 
Person locations (logits) 
Expected value 
Psoriasis 
Atopic Dermatitis
Example of DIF by gender 
Influences the clothes you can wear 
Expected value 
Person locations (logits) 
Females 
Males
Response thresholds
Response options 
• Four point response format 
 Very much 
 A lot 
 A little 
 Not at all 
Source of problem 
for items 4, 7 and 8 
Source of problem for 
items 6 and 9
Item Map 
Clustering of 
items 
Poor 
coverage of 
persons
Conclusions 
• DLQI – Pre-Rasch PRO 
• Rasch analysis highlighted several fundamental 
problems with DLQI 
• Problems probably result from inadequate scale 
development methodology 
• Concern for: 
- clinical trials 
- treatment decisions
Good PRO Design 
Item 
Reduction 
• Based on sound theoretical model 
• Cognitive debriefing interviews 
• Patient survey & application 
of Rasch analysis to data 
Draft 2 
Draft 3 
Scale 
Evaluation 
• Scaling properties 
• Classical psychometrics Draft 4 
Item 
Generation 
• Patient Interviews 
• Qualitative analysis Draft 1
References 
Finlay AY, Khan GK (1994). Dermatology Life Quality Index (DLQI)-a simple 
practical measure for routine clinical use. Clin Exp Dermatol 19: 210-6. 
Basra MKA, French R, Gatt RM, et al(2008). The dermatology Life Quality 
Index 1994-2007: a comprehensive review of validation and clinical results. Br 
J Dermatol 159: 997-1035 
Nijsten T, Meads DM, de Korte J et al (2007). Cross-Cultural Inequivalence of 
Dermatology-Specific Health related Quality of Life Instruments in Psoriasis 
Patients. Journal of Investigative Dermatology 127: 2315-2322 
Nijsten T, Meads DM, McKenna SP (2006). Dimensionality of the dermatology 
life quality index (DLQI): a commentary. Acta Derm Venereol 86:284-5; author 
reply 285-6.
Overall fit to the model 
Item-Trait 
interaction 
PSI Unidimensionality 
(CI) 
Items Persons 
Mean SD Mean SD 
0.01 0.85 -0.81 0.98 -0.30 0.81 0.03 (0.01 – 0.06)

More Related Content

Similar to Rasch analysis of the Dermatology Life Quality Questionnaire (DLQI)

1.Use the following guidelines to critique the research article
1.Use the following guidelines to critique the research article 1.Use the following guidelines to critique the research article
1.Use the following guidelines to critique the research article BenitoSumpter862
 
Basic.Method.pptx
Basic.Method.pptxBasic.Method.pptx
Basic.Method.pptxSundosHamza
 
Introduction to research methodology
Introduction to research methodologyIntroduction to research methodology
Introduction to research methodologymlogaraj
 
Presentation 1
Presentation 1Presentation 1
Presentation 1reinan19
 
RSS 2012 How to Write a Health Survey
RSS 2012 How to Write a Health SurveyRSS 2012 How to Write a Health Survey
RSS 2012 How to Write a Health SurveyWesam Abuznadah
 
Race to the Top Presentation on Integrated Units
Race to the Top Presentation on Integrated UnitsRace to the Top Presentation on Integrated Units
Race to the Top Presentation on Integrated UnitsArch Grieve
 
Getting started with a systematic review: developing your review question.
Getting started with a systematic review: developing your review question.Getting started with a systematic review: developing your review question.
Getting started with a systematic review: developing your review question.University of Liverpool Library
 
Addressing classroom diversity competency: A cross-cultural survey of pre-ser...
Addressing classroom diversity competency: A cross-cultural survey of pre-ser...Addressing classroom diversity competency: A cross-cultural survey of pre-ser...
Addressing classroom diversity competency: A cross-cultural survey of pre-ser...Centro de Investigaciones Educativas
 
Vittles - Quantified Self for Personal Health
Vittles - Quantified Self for Personal Health Vittles - Quantified Self for Personal Health
Vittles - Quantified Self for Personal Health Anne Everars
 
Developing a fundable research question: 27 June 2017
Developing a fundable research question: 27 June 2017 Developing a fundable research question: 27 June 2017
Developing a fundable research question: 27 June 2017 RDSLondon
 
Defining, classifying and measuring functioning and disability in DSM5
Defining,  classifying and measuring functioning and disability in DSM5Defining,  classifying and measuring functioning and disability in DSM5
Defining, classifying and measuring functioning and disability in DSM5Bedirhan Ustun
 
JPI Conference Dublin - Edvard Beem - Evaluation and Monitoring Framework
JPI Conference Dublin - Edvard Beem - Evaluation and Monitoring FrameworkJPI Conference Dublin - Edvard Beem - Evaluation and Monitoring Framework
JPI Conference Dublin - Edvard Beem - Evaluation and Monitoring Frameworkjpndresearch
 
Chapter 2Study DesignsLearning Objectives•.docx
Chapter 2Study DesignsLearning Objectives•.docxChapter 2Study DesignsLearning Objectives•.docx
Chapter 2Study DesignsLearning Objectives•.docxketurahhazelhurst
 
2.TOPIC SELECTION and standard operating procedure.pptx
2.TOPIC SELECTION and standard operating procedure.pptx2.TOPIC SELECTION and standard operating procedure.pptx
2.TOPIC SELECTION and standard operating procedure.pptx4negero
 
Utility and Added Value of Classifications in Health Information Systems
Utility and Added Value of Classifications in Health Information SystemsUtility and Added Value of Classifications in Health Information Systems
Utility and Added Value of Classifications in Health Information SystemsBedirhan Ustun
 
JPND Research Strategy presentation T. Gasser
JPND Research Strategy presentation  T. GasserJPND Research Strategy presentation  T. Gasser
JPND Research Strategy presentation T. Gasserjpndresearch
 

Similar to Rasch analysis of the Dermatology Life Quality Questionnaire (DLQI) (20)

1.Use the following guidelines to critique the research article
1.Use the following guidelines to critique the research article 1.Use the following guidelines to critique the research article
1.Use the following guidelines to critique the research article
 
Basic.Method.pptx
Basic.Method.pptxBasic.Method.pptx
Basic.Method.pptx
 
Introduction to research methodology
Introduction to research methodologyIntroduction to research methodology
Introduction to research methodology
 
presentation_1 (1).ppt
presentation_1 (1).pptpresentation_1 (1).ppt
presentation_1 (1).ppt
 
Presentation 1
Presentation 1Presentation 1
Presentation 1
 
RSS 2012 How to Write a Health Survey
RSS 2012 How to Write a Health SurveyRSS 2012 How to Write a Health Survey
RSS 2012 How to Write a Health Survey
 
Race to the Top Presentation on Integrated Units
Race to the Top Presentation on Integrated UnitsRace to the Top Presentation on Integrated Units
Race to the Top Presentation on Integrated Units
 
Getting started with a systematic review: developing your review question.
Getting started with a systematic review: developing your review question.Getting started with a systematic review: developing your review question.
Getting started with a systematic review: developing your review question.
 
Addressing classroom diversity competency: A cross-cultural survey of pre-ser...
Addressing classroom diversity competency: A cross-cultural survey of pre-ser...Addressing classroom diversity competency: A cross-cultural survey of pre-ser...
Addressing classroom diversity competency: A cross-cultural survey of pre-ser...
 
Vittles - Quantified Self for Personal Health
Vittles - Quantified Self for Personal Health Vittles - Quantified Self for Personal Health
Vittles - Quantified Self for Personal Health
 
Developing a fundable research question: 27 June 2017
Developing a fundable research question: 27 June 2017 Developing a fundable research question: 27 June 2017
Developing a fundable research question: 27 June 2017
 
judith dyson collaborative launch
judith dyson collaborative launchjudith dyson collaborative launch
judith dyson collaborative launch
 
Defining, classifying and measuring functioning and disability in DSM5
Defining,  classifying and measuring functioning and disability in DSM5Defining,  classifying and measuring functioning and disability in DSM5
Defining, classifying and measuring functioning and disability in DSM5
 
JPI Conference Dublin - Edvard Beem - Evaluation and Monitoring Framework
JPI Conference Dublin - Edvard Beem - Evaluation and Monitoring FrameworkJPI Conference Dublin - Edvard Beem - Evaluation and Monitoring Framework
JPI Conference Dublin - Edvard Beem - Evaluation and Monitoring Framework
 
Chapter 2Study DesignsLearning Objectives•.docx
Chapter 2Study DesignsLearning Objectives•.docxChapter 2Study DesignsLearning Objectives•.docx
Chapter 2Study DesignsLearning Objectives•.docx
 
2.TOPIC SELECTION and standard operating procedure.pptx
2.TOPIC SELECTION and standard operating procedure.pptx2.TOPIC SELECTION and standard operating procedure.pptx
2.TOPIC SELECTION and standard operating procedure.pptx
 
Session 4 logic models and indicators
Session 4   logic models and indicatorsSession 4   logic models and indicators
Session 4 logic models and indicators
 
Introduction to Research Methods in Education
Introduction to Research Methods in EducationIntroduction to Research Methods in Education
Introduction to Research Methods in Education
 
Utility and Added Value of Classifications in Health Information Systems
Utility and Added Value of Classifications in Health Information SystemsUtility and Added Value of Classifications in Health Information Systems
Utility and Added Value of Classifications in Health Information Systems
 
JPND Research Strategy presentation T. Gasser
JPND Research Strategy presentation  T. GasserJPND Research Strategy presentation  T. Gasser
JPND Research Strategy presentation T. Gasser
 

Recently uploaded

Call Girls in Adil Nagar 7001305949 Free Delivery at Your Door Model
Call Girls in Adil Nagar 7001305949 Free Delivery at Your Door ModelCall Girls in Adil Nagar 7001305949 Free Delivery at Your Door Model
Call Girls in Adil Nagar 7001305949 Free Delivery at Your Door ModelCall Girls Lucknow
 
independent Call Girls Sarjapur Road - 7001305949 with real photos and phone ...
independent Call Girls Sarjapur Road - 7001305949 with real photos and phone ...independent Call Girls Sarjapur Road - 7001305949 with real photos and phone ...
independent Call Girls Sarjapur Road - 7001305949 with real photos and phone ...narwatsonia7
 
Russian Call Girls Sadashivanagar | 7001305949 At Low Cost Cash Payment Booking
Russian Call Girls Sadashivanagar | 7001305949 At Low Cost Cash Payment BookingRussian Call Girls Sadashivanagar | 7001305949 At Low Cost Cash Payment Booking
Russian Call Girls Sadashivanagar | 7001305949 At Low Cost Cash Payment Bookingnarwatsonia7
 
Hi,Fi Call Girl In Marathahalli - 7001305949 with real photos and phone numbers
Hi,Fi Call Girl In Marathahalli - 7001305949 with real photos and phone numbersHi,Fi Call Girl In Marathahalli - 7001305949 with real photos and phone numbers
Hi,Fi Call Girl In Marathahalli - 7001305949 with real photos and phone numbersnarwatsonia7
 
Call Girls Ghaziabad 9999965857 Cheap and Best with original Photos
Call Girls Ghaziabad 9999965857 Cheap and Best with original PhotosCall Girls Ghaziabad 9999965857 Cheap and Best with original Photos
Call Girls Ghaziabad 9999965857 Cheap and Best with original Photosparshadkalavatidevi7
 
Experience learning - lessons from 25 years of ATACC - Mark Forrest and Halde...
Experience learning - lessons from 25 years of ATACC - Mark Forrest and Halde...Experience learning - lessons from 25 years of ATACC - Mark Forrest and Halde...
Experience learning - lessons from 25 years of ATACC - Mark Forrest and Halde...scanFOAM
 
Russian Escorts Delhi | 9711199171 | all area service available
Russian Escorts Delhi | 9711199171 | all area service availableRussian Escorts Delhi | 9711199171 | all area service available
Russian Escorts Delhi | 9711199171 | all area service availablesandeepkumar69420
 
Call Girls Service Bommasandra - Call 7001305949 Rs-3500 with A/C Room Cash o...
Call Girls Service Bommasandra - Call 7001305949 Rs-3500 with A/C Room Cash o...Call Girls Service Bommasandra - Call 7001305949 Rs-3500 with A/C Room Cash o...
Call Girls Service Bommasandra - Call 7001305949 Rs-3500 with A/C Room Cash o...narwatsonia7
 
2024 HCAT Healthcare Technology Insights
2024 HCAT Healthcare Technology Insights2024 HCAT Healthcare Technology Insights
2024 HCAT Healthcare Technology InsightsHealth Catalyst
 
Globalny raport: „Prawdziwe piękno 2024" od Dove
Globalny raport: „Prawdziwe piękno 2024" od DoveGlobalny raport: „Prawdziwe piękno 2024" od Dove
Globalny raport: „Prawdziwe piękno 2024" od Doveagatadrynko
 
Call Girls Hyderabad Krisha 9907093804 Independent Escort Service Hyderabad
Call Girls Hyderabad Krisha 9907093804 Independent Escort Service HyderabadCall Girls Hyderabad Krisha 9907093804 Independent Escort Service Hyderabad
Call Girls Hyderabad Krisha 9907093804 Independent Escort Service Hyderabaddelhimodelshub1
 
College Call Girls Hyderabad Sakshi 9907093804 Independent Escort Service Hyd...
College Call Girls Hyderabad Sakshi 9907093804 Independent Escort Service Hyd...College Call Girls Hyderabad Sakshi 9907093804 Independent Escort Service Hyd...
College Call Girls Hyderabad Sakshi 9907093804 Independent Escort Service Hyd...delhimodelshub1
 
FAMILY in sociology for physiotherapists.pptx
FAMILY in sociology for physiotherapists.pptxFAMILY in sociology for physiotherapists.pptx
FAMILY in sociology for physiotherapists.pptxMumux Mirani
 
MVP Health Care City of Schenectady Presentation
MVP Health Care City of Schenectady PresentationMVP Health Care City of Schenectady Presentation
MVP Health Care City of Schenectady PresentationMVP Health Care
 
Call Girls South Delhi 9999965857 Cheap and Best with original Photos
Call Girls South Delhi 9999965857 Cheap and Best with original PhotosCall Girls South Delhi 9999965857 Cheap and Best with original Photos
Call Girls South Delhi 9999965857 Cheap and Best with original Photosparshadkalavatidevi7
 
Air-Hostess Call Girls Shanti Nagar - Call 7001305949 Rs-3500 with A/C Room C...
Air-Hostess Call Girls Shanti Nagar - Call 7001305949 Rs-3500 with A/C Room C...Air-Hostess Call Girls Shanti Nagar - Call 7001305949 Rs-3500 with A/C Room C...
Air-Hostess Call Girls Shanti Nagar - Call 7001305949 Rs-3500 with A/C Room C...narwatsonia7
 
9711199012 Najafgarh Call Girls ₹5.5k With COD Free Home Delivery
9711199012 Najafgarh Call Girls ₹5.5k With COD Free Home Delivery9711199012 Najafgarh Call Girls ₹5.5k With COD Free Home Delivery
9711199012 Najafgarh Call Girls ₹5.5k With COD Free Home Deliverymarshasaifi
 
Russian Call Girls Hyderabad Saloni 9907093804 Independent Escort Service Hyd...
Russian Call Girls Hyderabad Saloni 9907093804 Independent Escort Service Hyd...Russian Call Girls Hyderabad Saloni 9907093804 Independent Escort Service Hyd...
Russian Call Girls Hyderabad Saloni 9907093804 Independent Escort Service Hyd...delhimodelshub1
 
Russian Call Girls in Goa Samaira 7001305949 Independent Escort Service Goa
Russian Call Girls in Goa Samaira 7001305949 Independent Escort Service GoaRussian Call Girls in Goa Samaira 7001305949 Independent Escort Service Goa
Russian Call Girls in Goa Samaira 7001305949 Independent Escort Service Goanarwatsonia7
 
Gurgaon DLF Phase 5 Call Girls ( 9873940964 ) Book Hot And Sexy Girls In A Fe...
Gurgaon DLF Phase 5 Call Girls ( 9873940964 ) Book Hot And Sexy Girls In A Fe...Gurgaon DLF Phase 5 Call Girls ( 9873940964 ) Book Hot And Sexy Girls In A Fe...
Gurgaon DLF Phase 5 Call Girls ( 9873940964 ) Book Hot And Sexy Girls In A Fe...ggsonu500
 

Recently uploaded (20)

Call Girls in Adil Nagar 7001305949 Free Delivery at Your Door Model
Call Girls in Adil Nagar 7001305949 Free Delivery at Your Door ModelCall Girls in Adil Nagar 7001305949 Free Delivery at Your Door Model
Call Girls in Adil Nagar 7001305949 Free Delivery at Your Door Model
 
independent Call Girls Sarjapur Road - 7001305949 with real photos and phone ...
independent Call Girls Sarjapur Road - 7001305949 with real photos and phone ...independent Call Girls Sarjapur Road - 7001305949 with real photos and phone ...
independent Call Girls Sarjapur Road - 7001305949 with real photos and phone ...
 
Russian Call Girls Sadashivanagar | 7001305949 At Low Cost Cash Payment Booking
Russian Call Girls Sadashivanagar | 7001305949 At Low Cost Cash Payment BookingRussian Call Girls Sadashivanagar | 7001305949 At Low Cost Cash Payment Booking
Russian Call Girls Sadashivanagar | 7001305949 At Low Cost Cash Payment Booking
 
Hi,Fi Call Girl In Marathahalli - 7001305949 with real photos and phone numbers
Hi,Fi Call Girl In Marathahalli - 7001305949 with real photos and phone numbersHi,Fi Call Girl In Marathahalli - 7001305949 with real photos and phone numbers
Hi,Fi Call Girl In Marathahalli - 7001305949 with real photos and phone numbers
 
Call Girls Ghaziabad 9999965857 Cheap and Best with original Photos
Call Girls Ghaziabad 9999965857 Cheap and Best with original PhotosCall Girls Ghaziabad 9999965857 Cheap and Best with original Photos
Call Girls Ghaziabad 9999965857 Cheap and Best with original Photos
 
Experience learning - lessons from 25 years of ATACC - Mark Forrest and Halde...
Experience learning - lessons from 25 years of ATACC - Mark Forrest and Halde...Experience learning - lessons from 25 years of ATACC - Mark Forrest and Halde...
Experience learning - lessons from 25 years of ATACC - Mark Forrest and Halde...
 
Russian Escorts Delhi | 9711199171 | all area service available
Russian Escorts Delhi | 9711199171 | all area service availableRussian Escorts Delhi | 9711199171 | all area service available
Russian Escorts Delhi | 9711199171 | all area service available
 
Call Girls Service Bommasandra - Call 7001305949 Rs-3500 with A/C Room Cash o...
Call Girls Service Bommasandra - Call 7001305949 Rs-3500 with A/C Room Cash o...Call Girls Service Bommasandra - Call 7001305949 Rs-3500 with A/C Room Cash o...
Call Girls Service Bommasandra - Call 7001305949 Rs-3500 with A/C Room Cash o...
 
2024 HCAT Healthcare Technology Insights
2024 HCAT Healthcare Technology Insights2024 HCAT Healthcare Technology Insights
2024 HCAT Healthcare Technology Insights
 
Globalny raport: „Prawdziwe piękno 2024" od Dove
Globalny raport: „Prawdziwe piękno 2024" od DoveGlobalny raport: „Prawdziwe piękno 2024" od Dove
Globalny raport: „Prawdziwe piękno 2024" od Dove
 
Call Girls Hyderabad Krisha 9907093804 Independent Escort Service Hyderabad
Call Girls Hyderabad Krisha 9907093804 Independent Escort Service HyderabadCall Girls Hyderabad Krisha 9907093804 Independent Escort Service Hyderabad
Call Girls Hyderabad Krisha 9907093804 Independent Escort Service Hyderabad
 
College Call Girls Hyderabad Sakshi 9907093804 Independent Escort Service Hyd...
College Call Girls Hyderabad Sakshi 9907093804 Independent Escort Service Hyd...College Call Girls Hyderabad Sakshi 9907093804 Independent Escort Service Hyd...
College Call Girls Hyderabad Sakshi 9907093804 Independent Escort Service Hyd...
 
FAMILY in sociology for physiotherapists.pptx
FAMILY in sociology for physiotherapists.pptxFAMILY in sociology for physiotherapists.pptx
FAMILY in sociology for physiotherapists.pptx
 
MVP Health Care City of Schenectady Presentation
MVP Health Care City of Schenectady PresentationMVP Health Care City of Schenectady Presentation
MVP Health Care City of Schenectady Presentation
 
Call Girls South Delhi 9999965857 Cheap and Best with original Photos
Call Girls South Delhi 9999965857 Cheap and Best with original PhotosCall Girls South Delhi 9999965857 Cheap and Best with original Photos
Call Girls South Delhi 9999965857 Cheap and Best with original Photos
 
Air-Hostess Call Girls Shanti Nagar - Call 7001305949 Rs-3500 with A/C Room C...
Air-Hostess Call Girls Shanti Nagar - Call 7001305949 Rs-3500 with A/C Room C...Air-Hostess Call Girls Shanti Nagar - Call 7001305949 Rs-3500 with A/C Room C...
Air-Hostess Call Girls Shanti Nagar - Call 7001305949 Rs-3500 with A/C Room C...
 
9711199012 Najafgarh Call Girls ₹5.5k With COD Free Home Delivery
9711199012 Najafgarh Call Girls ₹5.5k With COD Free Home Delivery9711199012 Najafgarh Call Girls ₹5.5k With COD Free Home Delivery
9711199012 Najafgarh Call Girls ₹5.5k With COD Free Home Delivery
 
Russian Call Girls Hyderabad Saloni 9907093804 Independent Escort Service Hyd...
Russian Call Girls Hyderabad Saloni 9907093804 Independent Escort Service Hyd...Russian Call Girls Hyderabad Saloni 9907093804 Independent Escort Service Hyd...
Russian Call Girls Hyderabad Saloni 9907093804 Independent Escort Service Hyd...
 
Russian Call Girls in Goa Samaira 7001305949 Independent Escort Service Goa
Russian Call Girls in Goa Samaira 7001305949 Independent Escort Service GoaRussian Call Girls in Goa Samaira 7001305949 Independent Escort Service Goa
Russian Call Girls in Goa Samaira 7001305949 Independent Escort Service Goa
 
Gurgaon DLF Phase 5 Call Girls ( 9873940964 ) Book Hot And Sexy Girls In A Fe...
Gurgaon DLF Phase 5 Call Girls ( 9873940964 ) Book Hot And Sexy Girls In A Fe...Gurgaon DLF Phase 5 Call Girls ( 9873940964 ) Book Hot And Sexy Girls In A Fe...
Gurgaon DLF Phase 5 Call Girls ( 9873940964 ) Book Hot And Sexy Girls In A Fe...
 

Rasch analysis of the Dermatology Life Quality Questionnaire (DLQI)

  • 1. Rasch analysis of the Dermatology Life Quality Questionnaire (DLQI) James Twiss and Stephen McKenna Galen Research Ltd, Manchester, UK Email: jtwiss@galen-research.com
  • 2. Objectives • To discuss good scale development methodology in the context of Rasch analysis • Example - Dermatology Life Quality Index (DLQI)
  • 3. The DLQI • 10-item generic dermatology Patient Reported Outcome (PRO) measure • Scored 0-30. High scores=worse • Used with 30 different skin conditions • Available in 55 languages • Used for treatment selection in the UK
  • 4. DLQI development • Uses patient reports of problems • 49 identified ‘aspects’ condensed into 10 items • Designed to fit on one side of A4 • Items phrased to include additional aspects
  • 5. The DLQI - content Sample DLQI items: Over the last week… how embarrassed or self conscious have you been because of your skin? how much has your skin interfered with you going shopping or looking after your home or garden? how much has your skin made it difficult for you to do any sport? how much of a problem has the treatment for your skin been, for example by making your home messy, or by taking up time?
  • 6. The DLQI – response format • Four point response format – Very much – A lot – A little – Not at all • 8 items also have a ‘Not relevant’ option
  • 7. Psychometric properties • Classical psychometric properties adequate (Basra et al, 2008) • One previous Rasch analysis compared 6 language versions (Nijsten and Meads, 2007) – Overall misfit to the model – Misfit in 3 individual countries – DIF by country for every item
  • 8. Study aims • Rasch analysis of DLQI data from two patient groups: - atopic dermatitis - psoriasis • Relate results to development methods used for DLQI
  • 9. Analyses Rasch analysis employed RUMM2020 • Overall fit to model • Individual Item fit • Response threshold order • DIF by age and gender • DIF by disease (AD vs psoriasis) • Item-trait coverage
  • 10. Sample Psoriasis (n = 146) Atopic Dermatitis (n = 146) Gender (%) Male 73 (50) 73 (50) Female 73 (50) 73 (50) Age (Years) Mean (SD) 44.4 (14.7) 45.5 (16.6) Range 66 (17-83) 62 (20-82) Duration (years) Mean (SD) 20.9 (13.5) 28.2 (17.5) Range 67 (2-69) 76 (0-76)
  • 11. DLQI scores Psoriasis Atopic dermatitis Mean (SD) 8.8 (6.7) 6.1 (4.6) Median (IQR) 7 (3.0-12.3) 5 (3-8) Range 29 (0-29) 26 (0-26)
  • 12. Overall fit to the Rasch model Initial fit statistics (partial credit model) Item-trait interaction PSI Items Persons Mean SD Mean SD 0.85 0.98 -0.30 0.81 0.01 -0.81
  • 13. Item fit Item description Location Fit residual Chi2 p value 1. itchy, sore, painful or stinging -1.61 -0.03 3.4 0.50 2. embarrassment/self consciousness -0.52 -1.97 15.0 3. interferes with shopping/looking after home/garden 0.005* 0.99 -1.18 3.8 0.44 4. influences choice of clothes -0.54 -0.14 4.4 0.35 5. affects social/leisure activities 0.32 12.7 6. affect ability to do sport -0.02 0.29 3.0 0.56 7. prevents working/studying 0.25 0.23 12.6 8. creates problems with partner/close friends/relatives -2.69 0.01 0.01 0.59 -0.89 2.1 0.72 9. causes sexual difficulties 0.89 -1.23 2.2 0.70 10. problems with treatment -0.36 -0.47 3.5 0.48
  • 14. Problems with items • 2 - Over the last week, how embarrassed or self conscious have you been because of your skin? • 5 - Over the past week, how much has your skin affected any social or leisure activities? • 7 - Over the past week, how much has your skin prevented you working / studying?
  • 15. DIF analysis Item description Uniform DIF Non-uniform DIF itchy, sore, painful or stinging Disease embarrassment/self consciousness Age group/Gender interferes with shopping/looking after home/garden Disease Disease influences choice of clothes Gender*/ Disease affects social/leisure activities Disease affect ability to do sport Gender Gender prevents working/studying Gender/Disease* creates problems with partner/close friends/relatives causes sexual difficulties problems with treatment Age group*
  • 16. Example of DIF by disease Prevents working or studying Person locations (logits) Expected value Psoriasis Atopic Dermatitis
  • 17. Example of DIF by gender Influences the clothes you can wear Expected value Person locations (logits) Females Males
  • 19. Response options • Four point response format  Very much  A lot  A little  Not at all Source of problem for items 4, 7 and 8 Source of problem for items 6 and 9
  • 20. Item Map Clustering of items Poor coverage of persons
  • 21. Conclusions • DLQI – Pre-Rasch PRO • Rasch analysis highlighted several fundamental problems with DLQI • Problems probably result from inadequate scale development methodology • Concern for: - clinical trials - treatment decisions
  • 22. Good PRO Design Item Reduction • Based on sound theoretical model • Cognitive debriefing interviews • Patient survey & application of Rasch analysis to data Draft 2 Draft 3 Scale Evaluation • Scaling properties • Classical psychometrics Draft 4 Item Generation • Patient Interviews • Qualitative analysis Draft 1
  • 23. References Finlay AY, Khan GK (1994). Dermatology Life Quality Index (DLQI)-a simple practical measure for routine clinical use. Clin Exp Dermatol 19: 210-6. Basra MKA, French R, Gatt RM, et al(2008). The dermatology Life Quality Index 1994-2007: a comprehensive review of validation and clinical results. Br J Dermatol 159: 997-1035 Nijsten T, Meads DM, de Korte J et al (2007). Cross-Cultural Inequivalence of Dermatology-Specific Health related Quality of Life Instruments in Psoriasis Patients. Journal of Investigative Dermatology 127: 2315-2322 Nijsten T, Meads DM, McKenna SP (2006). Dimensionality of the dermatology life quality index (DLQI): a commentary. Acta Derm Venereol 86:284-5; author reply 285-6.
  • 24. Overall fit to the model Item-Trait interaction PSI Unidimensionality (CI) Items Persons Mean SD Mean SD 0.01 0.85 -0.81 0.98 -0.30 0.81 0.03 (0.01 – 0.06)

Editor's Notes

  1. Aim: to discuss how problems identified during Rasch analysis can be used to illustrate scale development issues
  2. One of the most popular HRQoL measures in Dermatology NICE guidelines & Health Technology Assessment (HTA) Developed in 1994 before the wide use of Rasch analysis in the area of health outcomes
  3. Here in lies several of the problems. Too much condensing of information. Too many ideas are squeezed into each item. Items should be simple, clear and contain only one idea. This is important from the perspective of Rasch analysis. Failure to follow this produces scales which have built in error. No theoretical model
  4. The content of the DLQI mainly covers issues related to functioning There is one emotional related item You can also see from this the items try to cover several areas in one item
  5. One may argue that items should not be included if they are not relevant to some of the patients A side issue is that individuals who answered not relevant were given the same score as those that answered ‘not at all’
  6. Psoriasis sample from the Manchester Psoriasis Service at Hope Hospital Atopic Dermatitis sample from the National Eczema society
  7. Mean fit residual for item-person interaction was extreme indicating misfit to the Rasch model. Shows the degree of divergence between the expected and actual data for each item. Transformed into a Z-score. Unidimensionality t-test was fine – suggesting that there was not multiple factors within the scale – Everett Smith (2002)
  8. Items 2, 5 and 7 all have some indication of problems
  9. Item 2 – Why does this item not fit the Rasch model? – Is it because this is the only emotional item? It is possible that it just doesn’t fit with the other items Item 5 – This is a very poorly worded item. The target audience would not use this kind of language. This may not be the reason for the item problem but it certainly doesn’t help. Items should be simple and in a language that is easy for respondents to relate to.
  10. It is unclear exactly why this item showed DIF by working or studying. This does, however, suggest that scores for participants with different kinds of skin conditions should not be combined
  11. DLQI 4 – obvious gender bias with the item If data were Rasch analysed during the development stage then some of these issues could have been addressed Category probability curve
  12. Several items with disordered response thresholds Response option 2 ‘a lot’ is also poorly defined in all items
  13. Response threshold issues were due to poor response option choices ‘Not relevant’ responders were scored the same as ‘not at all’ responders Results could underestimate problems with scoring of the response options Ambiguous nature of some of the items may have contributed to some of the problems
  14. This another issue which could again have been highlighted at the development stage
  15. DLQI scores cannot be compared across diseases without splitting of items The DLQI lacks items covering mild levels of HRQoL in dermatological conditions Problematic scaling issues are due to fundamental problems with the DLQI development
  16. Based on these findings it has been shown how failure to follow principals of good questionnaire design can lead to inbuilt error into the scale Simple and clear items, good measurement spread, items that are relevant, good response options, free from DIF