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Stephen McKenna & James Twiss
Galen Research Ltd, Manchester, UK
Email: smckenna@galen-research.com
Quality in item genera...
Creating a scale
Let’s create a new scale ……..
We need to write a lot of items and then apply Rasch
analysis
Introduction
• But what will it really measure?
• How relevant will the items be to respondents?
The value of Rasch analys...
Random item generation
Impact of MS Impact of MS
QoL
QoL
Func
Satis
Symp
Targeted item generation based on model of
construct
Impact of MS
QoL
Impairment
• Loss or abnormality of psychological,
physiological or anatomical structure or
function
• Equates to symptoms...
Disability (activity limitation)
• Any restriction or lack of ability to perform an
activity in the manner or within the r...
What is quality of life?
• Not symptoms, activity limitations, utility or clinical
outcome
• Uniquely patient-based
• Holi...
“Human life quality is
dependent upon the
satisfaction of certain
basic needs - lack of
disease, mobility,
adequate nutrit...
Item generation
• Appropriate source of items
• not existing measures
• not the literature
• not test-developers
• not cli...
Item generation
• Qualitative unstructured interviews
• focus groups do not work well
• do not start with a list of issues...
Item reduction
Ensure items assess the required construct. Remove items that:
– are poorly worded
– express more than one ...
PRIMUS
• Patient Reported Indices of Multiple Sclerosis (PRIMUS)
• consists of 3 scales:
• Symptoms (impairment)
• Activit...
Sample items from the PRIMUS QoL scale
• I feel I am a burden to others
• I have little freedom to do what I want to do
• ...
Rogues gallery – SF-36
• Does your health now limit you in vigorous activities, such as running, lifting
heavy objects, pa...
Rogues gallery – EQ-5D
5 items – adequate coverage?
Mobility
I have no problems in walking about
I have some problems in w...
Rogues gallery - WHOQOL
Do you get the kind of support from others that you need?
Are you able to accept your bodily appea...
Rogues gallery - DLQI
Over the last week, how much has your skin interfered
with you going shopping or looking after your ...
DLQI (not at all, a little, a lot, very much)
DLQI: DIF by gender
Influences the clothes you can wear
Expectedvalue
Person locations (logits)
Females
Males
Hypomanic Personality Scale: DIF by gender
‘I find it easy to get people sexually interested in me’
FIS: DIF by age
I have to rely more on others to help me or do things for me
CES-D: DIF by country
‘I was happy’
DLQI: DIF by disease
Prevents working or studying
Person locations (logits)
Expectedvalue
Psoriasis
Atopic Dermatitis
Conclusions
Quality of patient reported outcome scale depends on:
• Coherent and valid measurement model
• Quality item ge...
Great - now we can make an excellent scale with
the help of Rasch!
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The importance of quality in item generation; a prerequisite for Rasch analysis

The quality of a patient reported outcome scale depends on: a coherent and valid measurement model, quality item generation, and a simple response format.

After these criteria are met, we can think about fit to the Rasch model.

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The importance of quality in item generation; a prerequisite for Rasch analysis

  1. 1. Stephen McKenna & James Twiss Galen Research Ltd, Manchester, UK Email: smckenna@galen-research.com Quality in item generation; a prerequisite for Rasch analysis
  2. 2. Creating a scale Let’s create a new scale …….. We need to write a lot of items and then apply Rasch analysis
  3. 3. Introduction • But what will it really measure? • How relevant will the items be to respondents? The value of Rasch analysis is in perfecting the scale- not in generating its content
  4. 4. Random item generation Impact of MS Impact of MS QoL QoL Func Satis Symp
  5. 5. Targeted item generation based on model of construct Impact of MS QoL
  6. 6. Impairment • Loss or abnormality of psychological, physiological or anatomical structure or function • Equates to symptoms • Disturbances at level of organ • Fatigue, pain, dizziness, depression, sleep problems
  7. 7. Disability (activity limitation) • Any restriction or lack of ability to perform an activity in the manner or within the range considered normal for a human being • Equates to functioning or functional status • E.g. restricted mobility, problems dressing & bathing, social restrictions, problems showing affection • HRQL measures (such as SF-36) commonly assess functioning in addition to impairment
  8. 8. What is quality of life? • Not symptoms, activity limitations, utility or clinical outcome • Uniquely patient-based • Holistic – overall impact of disease and its treatment on the patient • Unidimensional
  9. 9. “Human life quality is dependent upon the satisfaction of certain basic needs - lack of disease, mobility, adequate nutrition and shelter.” Sir Thomas More (1478-1535)
  10. 10. Item generation • Appropriate source of items • not existing measures • not the literature • not test-developers • not clinicians in most cases • relevant patients
  11. 11. Item generation • Qualitative unstructured interviews • focus groups do not work well • do not start with a list of issues – only constructs • let the interviewee guide the interview as much as possible • audio-record and produce transcripts • invest a great deal of time analysing transcripts
  12. 12. Item reduction Ensure items assess the required construct. Remove items that: – are poorly worded – express more than one idea – appear difficult to translate – are personal to one interviewee – will not apply to all respondents; sex, employment etc – are likely to produce DIF; interest in shopping, attending gyms etc – are specific to one national culture – are facts or will not change: ‘I worry that my health will get worse’
  13. 13. PRIMUS • Patient Reported Indices of Multiple Sclerosis (PRIMUS) • consists of 3 scales: • Symptoms (impairment) • Activity limitations • Quality of life
  14. 14. Sample items from the PRIMUS QoL scale • I feel I am a burden to others • I have little freedom to do what I want to do • I have to push myself to do things • I avoid physical intimacy • I feel as if I have nothing to offer anyone
  15. 15. Rogues gallery – SF-36 • Does your health now limit you in vigorous activities, such as running, lifting heavy objects, participating in strenuous sports? – that rules out 95% of the British! Disliked by older respondents • General Health - How TRUE or FALSE are these statements for you? – I seem to get sick a little easier than other people – I am as healthy as anybody I know – I expect my health to get worse – My health is excellent Are these outcomes? MCS and PCS
  16. 16. Rogues gallery – EQ-5D 5 items – adequate coverage? Mobility I have no problems in walking about I have some problems in walking about I am confined to bed There seems to be a gap here! Anxiety/depression I am not anxious or depressed I am moderately anxious or depressed I am extremely anxious or depressed Are anxiety and depression the same constructs? What if I am anxious and depressed? What if I am moderately anxious and severely depressed?
  17. 17. Rogues gallery - WHOQOL Do you get the kind of support from others that you need? Are you able to accept your bodily appearance? How available to you is the information that you need? How satisfied are you with your access to health services? How satisfied are you with your transport? How safe do you feel in your daily life? Not health outcome as intended but static measure of QoL? The few relevant items are also poor: How satisfied are you with your sex life? How often do you have negative feelings, such as blue mood, despair, anxiety, depression?
  18. 18. Rogues gallery - DLQI Over the last week, how much has your skin interfered with you going shopping or looking after your home or garden? Over the last week, how much has your skin created problems with your partner or any of your close friends or relatives? 8/10 items can be answered not relevant (and scored ‘no problem’) Measure used to decide who should receive biologic treatment for psoriasis
  19. 19. DLQI (not at all, a little, a lot, very much)
  20. 20. DLQI: DIF by gender Influences the clothes you can wear Expectedvalue Person locations (logits) Females Males
  21. 21. Hypomanic Personality Scale: DIF by gender ‘I find it easy to get people sexually interested in me’
  22. 22. FIS: DIF by age I have to rely more on others to help me or do things for me
  23. 23. CES-D: DIF by country ‘I was happy’
  24. 24. DLQI: DIF by disease Prevents working or studying Person locations (logits) Expectedvalue Psoriasis Atopic Dermatitis
  25. 25. Conclusions Quality of patient reported outcome scale depends on: • Coherent and valid measurement model • Quality item generation • Simple response format Then we can think about fit to Rasch model
  26. 26. Great - now we can make an excellent scale with the help of Rasch!

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