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The valuation of disease-specific health states to facilitate economic

evaluation

• E. Kok, E. Stolk, Jan J. v. Busschbach

• Address:– Jan v. Busschbach

Erasmus University Rotterdaminstitute for Medical Technology Assessment (iMTA) PO box 17383000 DR Rotterdam+ 31-10-4088641+ 31-10-4088555 (secretariat)+ 31-10-4089092 (fax)Busschbach@bmg.eur.nl

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Quality of life measurement in health economics

• Preferred outcome: QALY

• Preferred perspective: societal– Values from the general public

– Values for imaginable health states

» (usually) not one own health state

• QALYS are often measured with standard questionnaires

– HUI or EQ-5D: standardized, validated

– Generic quality of life questionnaires

• Unfortunately, generic questionnaires are not sensitive for disease specific items

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Is EQ-5D sensitive in BPH?• MOBILITY

– I have no problems in walking about – I have some……. – I am confined to bed

• SELF-CARE– I have no problems with self-care – I have some problems….. – I am unable…

• USUAL ACTIVITIES– I have no problems with performing my usual

activities – I have some problems… – I am unable….

• PAIN/DISCOMFORT– I have no pain or discomfort – I have moderate ….. – I have extreme……..

• ANXIETY/DEPRESSION– I am not anxious or depressed – I am moderately……..– I am extremely…..

Not sensitive fo

r BPH

• BPH– Enlargement of the

prostate

– Causes voiding problems in elderly men

» Difficulties to pee

– Cure

» Operations

» New medicine suppress symptoms

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International Symptom Prostate Score

• The IPSS is often used as out come measure– Seen as valid and sensitive

• 7 questions: How often have you– had to push or strain to begin urination?– had a sensation of not emptying your bladder completely?– had to urinate again less than two hours after you finished urinating?– found you stopped and started again several times when you urinated?– you find it difficult to postpone urination?– had a weak urinary stream?– How many times did you most typically get up to urinate from the time you went to bed at night until

the time you got up in the morning?

• 6 answer levels– 0 = not at all (none)– 1 = seldom (one time)– 2 = less than half the time (two times)– 3 = about half the time (three times)– 4 = more than half the time (four times)– 5 = almost always (five or more times)

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Can we convert the IPSS outcomes into utilities?

• Attribute TTO values to the IPSS health states

• Problem: IPSS has 279.936 health states– 7 items, 6 answer levels = 67= 279.936

– Too many to value with TTO

• Reduce number of health states– Reduce items

» Factor analysis

– Reduce answer levels

» Combine answer levels

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• Factor analysis on patients IPSS responses – N = 1414

• Two main factors– Obstructive (alpha= 0.8018)– Irritative (alpha= 0.7165)

» Confirmed in literature

• Factors divided in 3 levels• Number of health states reduced to 33 = 9

– Can be valued directly

• TTO– General public, representative for gender/age (N=170)

Reduce number of health states

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QALY weights for BPH

almost always

sometimes

seldom/never

almost alwayssometimes

seldom/never

0,5

0,55

0,6

0,65

0,7

0,75

0,8

0,85

0,9

0,95

1

utilities (TTO)

obstructive

irritative

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How to come to these values?

Obstructive score Sum (IPSS1 + IPSS2 +IPSS4 + IPSS6)

Irritative score Sum (IPSS3 + IPSS5 +IPSS7)

Answer levels:

Domain score Level

Obstructive ( <= 4) Obstructive 1

( >= 5 & <= 16) Obstructive 2

( >= 17) Obstructive 3

Irritative (<= 3) Irritative 1

( >= 4 & <= 9) Irritative 2

( >= 10) Irritative 3

irritative

1.00 .97 .95 1

.97 .94 .92 2

.92 .90 .87 3

1 2 3

Obstructive

As example: obstructive 1 and irritative 2 = uti 1_2

Quality of life values:

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Treatment-effect

0,9

0,91

0,92

0,93

0,94

0,95

0,96

0,97

0,98

baseline follow up

uti

litie

s

surgery (n= 144) alpha-blockers (n=33)

finasteride (n=35) watchful waiting (n=159)

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How to interpret disease specific utilities

• Only the disutility of the specific disease is valued

• Generic and specific utilities are not on the same scale

– Generic top anchor: absence of any impairment

– Specific top anchor: absence of specific impairment

» Co morbidity might still be present

• Value of life years “traded off” in TTO differ– Healthy subject: 1 life year is 1.0 QALY

– Sick subject: 1 life year is 0.5 QALY

– Life years of healthy persons are more worth than those of sick

• Correction for co morbidity needed

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Specific values should be corrected for average morbidity

• Overall health states influence disutility– 20% trade off at 1.00: disutility = 0.20

– 20% trade off at 0.80: disutility = 0.16

– 20% trade off at 0.60: disutility = 0.12

• Raw specific trade-off might overestimated gains– Also counts for so called “scenarios”

– Overestimated CE-ration by 15% using specific utilities

» Proposed by Fryback & Lawrence, MDM 1997

» For not completely the same problem…

» …for own health states, not imaginable health states

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Solution: multiplicative model

• Related specific utilities to generic– Values of the IPSS have to be multiplied by average value for age

group.

» For instance male age 55-64: overall QoL utility: 0.81

» Most severe BPH: 0.87

» Male age 55-64 with most severe BPH: 0.81 x 0.87 = .7047

• Maximum gain reduces from – Raw score 1.00 - 0.87 = 0.13

– Adjust score 0.81 - 0.70 = 0.11

– 15 % reduction

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• We validated the IPSS for the use in economic appraisal

– Now, IPSS has QALY-weights

– New and already published research can be converted into QALYs

• Many other applications possible – Also in erectile dysfunction and diabetic foot ulcers

• Advantage use specific QALYs measures– High sensitive disease specific measures for QALY-analysis

• Disadvantages– ± 15 % correction needed

Conclusion