Economic evaluation of health programmes

Department of Epidemiology, Biostatistics and Occupational Health

Class no. 11: Cost-utility analysis – Part 4Oct 8, 2008

Plan of classFinish material from last classPreference-based generic instrumentsConstruction of QALYsLimitations of QALYsQALYs vs DALYs

Preference-based generic instruments: Purpose

SG, TTO difficult and costly to useOne would prefer a simpler instrumentAdminister to subjects in a study to

evaluate their health-related quality of life as rated by a community sample

Preference-based generic instruments: 2 steps in use

QUESTIONNAIRE THAT ASKS AT WHICH OF 3 TO 6 LEVELS RESPONDENT IS ON 5

TO 15 DIMENSIONS

FORMULA FOR CONVERTING RESPONSES INTO A HEALTH RELATED QUALITY OF LIFE WEIGHT FROM 0 TO 1

(VALUE OR UTILITY DEPENDING ON QUESTIONNAIRE)

Questionnaire design

Obvious differences: Number and choice of dimensions Number of levels for each dimension

Instrument Dimensions Number of levels per dimension

Number of

statesQuality of well-being

Mobility, physical activity, social functioning27 symptoms/problems

32

945

EQ-5D Mobility, self-care, usual activities, pain/dicscomfort, anxiety/depression

3 243

SF-6D Physical functioning, role limitation, social functioning, pain, energy, mental health

4 – 6 18,000 (SF-36)7,500

(SF-12)

HUI2 Sensory, mobility, emotion, cognitive, self-care, painFertility

4 – 5

3

24,000

HUI3 Vision, hearing, speech, ambulation, dexterity, emotion, cognition, pain

5 – 6 972,000

Note: At least two other questionnaires exist: Australian Quality of Life (AQoL) and the Finnish 15D. Not as widely used as EQ-5D, SF-6D or HUI2 or HUI3. Not discussed in class.

Rheumatism Pain/Dexterity

Macular degene-

rationVision

LimitsWalking

Limits ability to read

Role, social and usual activities

Role, social and usual activities

Disease or disorder

Impairment Ability Participation

WHO international classification of health into disease or disorder, impairment, ability and participation (with examples). (Taken from Brazier et al., Measuring and valuing health benefits for economic evaluation, Oxford, 2007, Fig 4.1 )

Health as a spectrum

Rheumatism Pain/Dexterity

Macular degene-

rationVision

LimitsWalking

Limits ability to read

Role, social and usual activities

Role, social and usual activities

Disease or disorder

Impairment Ability Participation

HUI3

SF-6D, EQ-5D, HUI2

Include dimensions relating to social participation?

“Within skin” aspects of health: avoid measuring peoples’ choices/preferences “purer” measure of health No influence of adaptation

But general population values will underestimate adaptation

Health is a means, social participation part of its end – this is what matters to patients

Instrument Country where preferences obtained

Valuation technique

Quality of well-being

USA (San Diego) VAS

EQ-5D Belgium, Denmark, Finland, Germany, Japan, The Netherlands, Slovenia, Spain, UK, USA, Zimbabwe

TTO, VAS, ranking

SF-6D Hong Kong, Japan, UK, Australia, Brazil

SG, ranking

HUI2 Canada (Hamilton), UK VAS transformed into SG

HUI3 Canada (Hamilton), France VAS transformed into SG

Scoring the questionnaires

In each case, use a method such as SG, TTO, VAS to value some states, and interpolate statistically Too many states to value them all individually!

Two approaches to developing scoring methods: Multi-attribute utility theory (MAUT): HUI2,

HUI3 Statistical estimation without restrictive

assumptions of MAUT: QWB, SF-6D, EQ-5D

Multi-attribute utility theory: The problem

What happens when lottery outcome yields something that has several attributes, such as mobility, emotional state, etc?

How to combine the utilities of separate dimensions of outcome to generate an overall utility of the outcome?

Example

How would you combine utilities derived from an apartment that you might rent? Attributes include: (a) price; (b) location; (c) size; (d) quietness; (e) attractiveness; (f) other factors.

3 most common methods based on MAUT

In all cases, need to calculate utility associated with each dimension

Additive, multiplicative, multilinear (see formulas in book, p. 157)

The simpler the method, the more restrictive the assumptions e.g., additive implies no interactions

HUI2 and HUI3 use multiplicative formula

Exercises

On the EQ-5D, considering Table 6.4, what does score 11212 mean? What health-related quality of life weight does this represent?

On the HUI3, same questions for 22111223.

Choice of instrument matters

Different instruments yield different results Different ranges: -0.4 to 1.0 for EQ-5D, vs. 0.3 to 1.0

for SF-6D EQ-5D scores of 11111 can translate to SF-6D scores

as low as 0.56 Studies comparing scores across instruments for

same patients find significant differences• Patient group appears to be a factor

Differences as small as 0.03 should be considered significant

Reasons for differences Differences in coverage

Capacity vs functioning Symptoms, social health, mental health covered

differently Sensitivity of dimensions

Floor effect for physical and social functioning, role limitations for SF-6D

Ceiling effect with EQ-5D Valuation methods

Systematic differences depending on method

Choosing a method: Practicality

Instrument Comments on practicality – self-administeredQuality of well-being Somewhat more complex to fill out

EQ-5D Easiest to administer, very simple

SF-6D Usually derived from responses to SF-36 or SF-12 which are longer, lower completion rates

HUI2 Easy to administer, license costs

HUI3 Easy to administer, license costs

Choosing a method: Reliability

All have acceptable test-retest reliabilityDifferent responses depending on whether

patients or health professionals fill out – need to standardize to whom instrument administered

Choosing a method: Validity

QWB based on VAS HUI2 and HUI3 based on SG but as

transformation of VAS; not clear this is better than TTO used in EQ-5D

Populations from which data for scoring formulas derived are more or less comprehensive – more limited for HUIs, very broad for EQ-5D Unclear how important this is

Choosing a method: Conclusions

Differences in dimensions covered, number of levels, floor and ceiling effects may make one of the instruments more suitable for a particular patient group Which would you use for assessing cataract

surgery? Antidepressants?Use HUI3 rather than HUI2Don’t use QWB

A QALY exercise

With new cancer protocol: 6 months at HRQOL 0.3, followed by 15 years at 0.95

With standard treatment: 1 year at 0.5, followed by 7 years at 0.90, then 1 year at 0.8, 1 year at 0.5, then death

How many QALYs does the new protocol produce?

Limitations of QALYs (partial list)

Ignore priority often given to helping people at low initial state

Many small improvements to people at high initial state can be preferred to saving a life

Imperfectly measuredUse anyway?

QALYs vs DALYs (Disability-adjusted life years)

Feature QALYs DALYsLife expectancy measure Context-specific Longest in world

(Japanese women)

Disability weights Preferences (public or patients in study)

PTO scores from a panel of health care workers

Precision Continuous scores 7 states in addition to healthy or dead

Age weights? No Yes – lower weights for young and elderly

DALYs developed to do estimate potential impacts of possible health interventions in developing countries