Economic evaluation of health programmes Department of Epidemiology, Biostatistics and Occupational Health Class no. 11: Cost-utility analysis – Part 4 Oct 8, 2008

Plan of class  Finish material from last class  Preference-based generic instruments  Construction of QALYs  Limitations of QALYs  QALYs vs DALYs

Preference-based generic instruments: Purpose  SG, TTO difficult and costly to use  One would prefer a simpler instrument  Administer 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

InstrumentDimensionsNumber of levels per dimension Number of states Quality of well-being Mobility, physical activity, social functioning 27 symptoms/problems EQ-5DMobility, self-care, usual activities, pain/dicscomfort, anxiety/depression 3243 SF-6DPhysical functioning, role limitation, social functioning, pain, energy, mental health 4 – 618,000 (SF-36) 7,500 (SF-12) HUI2Sensory, mobility, emotion, cognitive, self- care, pain Fertility 4 – ,000 HUI3Vision, hearing, speech, ambulation, dexterity, emotion, cognition, pain 5 – 6972,000 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- ration Vision Limits Walking Limits ability to read Role, social and usual activities Disease or disorder ImpairmentAbilityParticipation 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- ration Vision Limits Walking Limits ability to read Role, social and usual activities Disease or disorder ImpairmentAbilityParticipation 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

InstrumentCountry where preferences obtained Valuation technique Quality of well-being USA (San Diego)VAS EQ-5DBelgium, Denmark, Finland, Germany, Japan, The Netherlands, Slovenia, Spain, UK, USA, Zimbabwe TTO, VAS, ranking SF-6DHong Kong, Japan, UK, Australia, Brazil SG, ranking HUI2Canada (Hamilton), UKVAS transformed into SG HUI3Canada (Hamilton), FranceVAS 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 mean? What health-related quality of life weight does this represent?  On the HUI3, same questions for

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 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 InstrumentComments on practicality – self-administered Quality of well-beingSomewhat more complex to fill out EQ-5DEasiest to administer, very simple SF-6DUsually derived from responses to SF-36 or SF-12 which are longer, lower completion rates HUI2Easy to administer, license costs HUI3Easy to administer, license costs

Choosing a method: Reliability  All have acceptable test-retest reliability  Different 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 HUI2  Don’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 measured  Use anyway?

QALYs vs DALYs (Disability- adjusted life years) FeatureQALYsDALYs Life expectancy measureContext-specificLongest in world (Japanese women) Disability weightsPreferences (public or patients in study) PTO scores from a panel of health care workers PrecisionContinuous scores7 states in addition to healthy or dead Age weights?NoYes – lower weights for young and elderly DALYs developed to do estimate potential impacts of possible health interventions in developing countries