VAS, SG, TTO and PTO Measuring quality of life An Interactive Introduction

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Quality of life



“…. Health is physical, mental and social well being and not merely the absence of disease or infirmity...”

 World Health Organization, 1947 

Extending health to well-being: Quality of life



What is the definition of quality of life?

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Many definitions

     Quality of life is the degree of need and satisfaction within the physical, psychological, social, activity, material and structural area (Hörnquist, 1982).

Quality of life is the subjective evaluation of good and satisfactory character of life as a whole (De Haes, 1988).

Health related quality of life is the subjective experiences or preferences expressed by an individual, or members of a particular group of persons, in relation to specified aspects of health status that are meaningful, in definable ways, for that individual or group (Till, 1992).

Quality of life is a state of well-being which is a composite of two components: 1) the ability to

perform

everyday activities which reflects physical psychological, and social well-being and 2) patient related symptoms (Gotay et al., 1992).

satisfaction

with levels of functioning and the control of disease and/or treatment An individual’s perception of their position in life in the context of the culture and values systems in which they live and in relation to their goals, expectations, standards and concerns (WHO Quality of life Groups, 1993).

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No clear definition



Researchers are free to choose



The notion of measuring the quality of life could include the measurement of practically anything of interest to anybody. And, no doubt, everybody could find arguments supporting the selection of whichever set of indicators to be his choice…

 Andrews & Withey, 1976, page 6 4

No clear definition because…



Different origins of research

 Clinical decision making • Does the patient benefit from the treatment?

 Epidemiology (public health) • what is the morbidity of the population?

 Health economics • Is it worth the money?

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Common items in definitions:



It is not the doctor who reports



Quality of life is subjective….

 “Given its inherently subjective nature, consensus was quickly reached that quality of life ratings should, whenever possible, be elicited directly from patients themselves. “ (Aaronson, in B Spilker (Ed): Quality of life and Pharmacoeconomics in Clinical Trails, 1996, page 180)  Reports between proxies and patients vary.

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Common items in definitions:



Health related



Multidimensional

 Physical, psychological, social 

Questionnaires

 Standardize questions and response • Reproducible results: sciences • Quantify subjectivity 

Operational defined

 Like IQ and temperature.

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How to measure quality of life form a clinical point of view?



Choose items

 Are you able to walk one kilometer ?

 Do you feel depressed ?



Choose response mode

 Binary   Multiple (Likert) Continuous ( Visual Analogue Scale ) yes / no yes / at bid / hardly / no Always ————

X

—— Never 

Combine items to dimensions of quality of life

 Sum up the items belonging to one dimension  Rescale sum on a scale from 0 to 100 8



Patient Items to value



Health state

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Uni-dimensional value



QALYs need a uni-dimensional value

 Like the IQ-test measures intelligence 

QALYs need a ratio or interval scale

 Difference 0.00 and 0.80 must be 8 time higher than 0.10



Five popular methods have these pretensions

 Visual analog scale     Time trade-off Standard gamble Person Trade-off Discrete Choice 10

Visual Analogue Scale



From psychological research

 Also called “category scaling”  Rescale from 0.00 to 1.00



Main critique

 No guarantee ratio scale  Lower value then face value 11

Time Trade-Off (TTO)



Wheelchair

 With a life expectancy: 50 years 

How many years would you trade-off for a cure?

 Max. trade-off is 10 years 

QALY(wheel) = QALY(healthy)

 Y * V(wheel) = Y * V(healthy)   50 V(wheel) = 40 * 1 V(wheel) = .80



Main critique

 Discounting effect  More complicated than VAS 12

Standard Gamble (SG)



Wheelchair

 Life expectancy is not important here 

How much are risk on death are you prepared to take for a cure?

 Max. risk is 20%   wheels = (100%-20%) life on feet V(Wheels) = 80% or .80



Main critique

 More complicated than VAS and TTO  Risk aversion 13

Health economists prefer TTO/SG



Visual analogue scale

 No trade-off: no relation to QALY  No interval proportions 

Standard Gamble / Time Trade-Off

 Trade-off: clear relation to QALY  Interval proportions 14

Values differ, but differences are often constant

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

12 11 1 11 21 1 21 11 1 11 12 1 11 11 2 11 12 2 32 21 1 21 23 2 33 32 1 22 32 3

EQ-5D health states

N = 103 students SG TTO VAS 22 23 3 33 33 3 15

Person Trade-Off



Values between patients

 Not ‘within’ a patient like VAS 

V(Q) = A / B



For instance:

 V(Q) = 100/300  V(Q) = 0.33

100 persons additionally 1 healthy year ?? persons 1 year free from disease Q 16

Person Trade-Off (PT0)



Values between patients

 Not ‘within’ a patient like SG, TTO and VAS 

For instance:

 300 V(Q) = 100 V(Full Health)   300 V(Q) = 100 * 1.00

V(Q) = 0.33

100 persons additionally 1 healthy year ?? persons 1 year free from disease Q 17

Incorporation of solidarity



Values between patients

 Not ‘within’ a patient like SG, TTO and VAS  Suggested for health priority setting 

Burden of Disease project

 WHO  Chris Murray, Eric Nord 18

PTO gives low values

0,4 0,2 0,0 1,0 0,8 0,6 TTO PTO Qu adri ple Se gia ve r de Stro pre ssi ke on (mo Se ve dera re st able te imp Se ve re a an airme gina nt) Diffi sth ma cu lt to Chro co nic ntro l dia Dise low er b bete ase s fre ack Visi e bre pain on d ast iso rde ca r (mi nce r ld to mo dera te) 19

Questionable psychometrics



Paul Kind:



If we look at TTO and PTO...

 we see that one of them is wrong 

If we look at PTO alone...

 We still see that one of them is wrong...

TTO PTO PTO

PTO is not a quick fix

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First markers WHO look better

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Smoothing by consensus

King CH (2008) Asymmetries of Poverty: Why Global Burden of Disease Valuations Underestimate the Burden of Neglected Tropical Diseases. PLoS Negl Trop Dis 2(3): e209.

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Replication PTO

Stouthard et al. Eur J Public Health 2000; 10: 24-30 23

PTO uses calibrated VAS

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Vos T, et al., 1999

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Essink-Bot et al., Cross-national comparability of burden of disease estimates: the European Disability Weights Project.

Bull World Health Organ. 2002;80(8):644-52.

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Validity of PTO



Health economists have a complex relation with PTO

 Unclear incorporation of equity (solidarity)   Bad psychometric proportions Unclear use of consensus by expert panels 

Not preferred

 But often used, as values for many health state are available 27

Discrete Choice Experiments (DCE)



State 1

 Moderate  problems in walking about Some problems washing or dressing  Some problems with performing usual activities   Some pain or discomfort No psychosocial problems 

State 1

 Some  problems in walking about Moderate problems washing or dressing  Some problems with performing usual activities   Some pain or discomfort No psychosocial problems 28

Preference relate to distance

A B 20% state A; 80% state B A B 30% state A; 70% state B 45% state A; 55% state B A B B A 80% state A; 20% state B

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DQI meet de kwaliteit van leven van personen met dementie op basis van vragen over 6 domeinen

Geheugen Oriëntatie Zelfzorg Lichamelijke gezondheid 1 2 3 1 2 3 1 2 3 1 2 3 Geen problemen Enige problemen Ernstige problemen Geen problemen Enige problemen Ernstige problemen Geen problemen Enige problemen Ernstige problemen Geen problemen Enige problemen Ernstige problemen Sociaal functioneren 1 2 3 Geen problemen Enige problemen Ernstige problemen Stemming 1 2 3 Geen problemen Enige problemen Ernstige problemen Bijvoorbeeld, een scorecombinatie van 121122 betekent de volgende gezondheidstoestand: Geen geheugenproblemen Enige oriëntatieproblemen Geen problemen met de zelfzorg Geen problemen met de lichamelijke gezondheid Enige problemen met sociaal functioneren Enige stemmingsproblemen Bron: Scholzel et. Al. Health and Quality of Life Outcomes 2012 Rosan Oostveen

Elke gezondheidtoestand zegt iets over de kwaliteit van leven Best = 0

0,0 -0,5 -1,0 -1,5 -2,0 -2,5 -3,0 • • Uit positie op meetlat is voor iedere gezondheidsdomein aan ieder antwoord een wegingsfactor toegekend aan de score Hoe groter de invloed van een score op een domein op de kwaliteit van leven, hoe hoger de wegingsfactor -3,5 -4,0

Slechtst = -3,98 Domeinen DQI

Lichamelijke gezondheid Geheugen Zelfzorg Stemming Sociaal functioneren Orientatie

Totaalscore

Ernstige problemen (3)

-0,82 -0,80 -0,71 -0,59 -0,57 -0,49

-3,98

Enige problemen (2)

-0,18 -0,23 -0,21 -0,11 -0,17 -0,08

-0,98

• De totaalscore op kwaliteit van leven van een dementerende is een optelling van de wegingsfactoren per vraag. De antwoorden van de persoon met dementie bepalen de wegingsfactoren

Geen problemen (1)

0 0 0 0 0 0

0

Bron: Scholzel et. Al. Health and Quality of Life Outcomes 2012

Little difference between Cost/Life Year and Cost/QALY

Richard Chapman et al, 2004, Health Economics

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Difference in QALYs makes little difference in outcome



Richard Chapman et al, 2004

 “In a sizable fraction of cost-utility analyses, quality adjusting did not substantially alter the estimated cost-effectiveness of an intervention, suggesting that sensitivity analyses using ad hoc adjustments or 'off-the-shelf' utility weights may be sufficient for many analyses.”  “The collection of preference weight data should […] should only be under-taken if the value of this information is likely to be greater than the cost of obtaining it.” 33

QALYs make a difference when:



Chronic disease



Palliative



Long term negative consequences

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