药物经济学中效用的基本概念

x
(worse)
Healthy
LIFE ‘B’
Health state i (better)
V (Hi) 1 (1V (Hj)) x t
t
Healthy
V(Hi)=0.6+0.4V(Hj)
Discrete choice experiment (DCE)
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DCE
o An attribute-based approach to collected stated preference
Designed to obtain comparable scores to the SG
How much time a respondent would like to give up to be in a healthier state compared to a less health state
o What is the “utility” in cost utility analysis?
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Health utility
A single measure for multiple (composite?) health outcomes (i.e. effectiveness, and side effects)
LIFE ‘A’ x
Full health
t
Loneliness
LIFE ‘B’
Death
U(full health)*x +U(loneliness)*(t-x)= 0 U(loneliness)= - 0.25
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TTO- temporary states
LIFE ‘A’
Health state j
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Steps for direct measurement
Step One
Developing health state descriptions
Step Two
Eliciting preferences
Step Three
Calculating health utilities
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Visual Analogue Scale (VAS)
Death p
Ti
step 2: ×
×
Healthy
×
Value of Ti on a scale from 0 (death) to 1 (healthy): V(Ti) = p/10
Value of Tj on a scale from 0 (death) to 1 (healthy): V(Tj) = p/10+ (m/10)((10-p)/10) = 0.3+0.28 = 0.58
Anchored at 0 for dead and 1 for full health
Comparability across different treatments or diseases
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von Neumann-Morgenstern utility theory
“A mathematical decision theory describing how a rational individual should make decisions when faced with uncertain outcomes.”
2
Preference, value, utility
o Preference is greater liking/desire toward something over others
o Value measures preference under certainty
o Utility measures preference under uncertainty
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VAS
➢ A respondent ranks health states according to his/her preference and then places them on a line or scale
➢ Interval or spacing between placements corresponds to the difference in preference as perceived by that respondent
von Neumann and Morgenstern 1944
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Axioms of vNM utility theory
o Existence and transitivity of preference A › B or A ‹ B or A ~ B If A › B and B › C , then A › C If A ~ B and B ~ C , then A ~ C
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How to measure health utilities?
With established elicitation techniques Direct measure ▪ Designing your own questionnaire/protocol ▪ Applying directly elicitation techniques Indirect measure ▪ Use of established questionnaire ▪ Calculating health utilities using scoring algorithms based on elicitation techniques
=1 1-p
=0.8 p
=0
The greater a person’s willingness to accept
the risk of death to avoid living in a health state, then the lower is the utility for that health state to him/her.
Loneliness
CHOICE “B”
100
% chance
Death
p*U(full health) + (1 - p)*U(loneliness)=0 24
CHOICE “A”
SG – temporary states
25
% chance
75
% chance
C
0.25 0.75
Healthy
o Rooted in the economic theory of random utility maximization
o Originally developed in transport economics and marketing research
o Measuring preference under certainty or uncertainty
Measuring preference under certainty
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LIFE ‘A’
TTO - chronic states
x
Full health
Death
LIFE ‘B’
Insomnia
U(insomnia)=x/t
t
Death
U(insomnia)=0.5 28
TTO –worse than death states
m
Death
×
d
Insomnia
×
ppΒιβλιοθήκη Full health×
U(insomnia) = (m-d)/(p-d) = 0.38
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VAS - temporary states
m
step 1: ×Ti
Tj
×
Healthy
×
Value of Tj on a scale from 0 (Ti) to 1 (healthy): V(Tj) = m/10
Without established elicitation techniques ▪ Judgment
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Direct measures
Visual analogue scale (VAS) Standard gamble (SG) Time trade-off (TTO) Discrete choice experiment (DCE)
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Risk-based choices in SG questions
Finding p such that: U (Hi)= pU(HFull health) +(1-p)U(Hdeath)
=p
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What does a utility tell…
CHOICE
Insomnia p Full health
o Independence of preference If A › B then pA +(1-p)C › pB +(1-p)C
o Continuity of preference If A › B and B › C, then existing a probability p, B ~ [pA +(1-p)C]
Health state j (worse)
CHOICE “B”
100
% chance
Health state i (better)
U(Hi)= p+ (1 - p)U(Hj)
U(Hi)= 0.25+0.75U(Hj)
Time trade-off (TTO)
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TTO
Developed specifically for use in health care by Torrance et al (1972).
SG-chronic states (cont’d)
CHOICE “A”
10
% chance
90
% chance
C
0.10 0.90
Full health
Death
CHOICE “B”
100
% chance
Insomnia
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CHOICE “A”
Worse than death?
0
% chance
Measuring health utilities for economic evaluation
What is utility?
o In economics, utility is a measure of relative satisfaction. It is a term referring to the total satisfaction received by a consumer from consuming a good or service.
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CHOICE “A”
SG- chronic states
90
% chance
10
% chance
90/10 C
10/90 0.90
…
0.10
50/50
Full health
CHOICE “B”
100
% chance
Death Insomnia
U(insomnia)= p/100 U(insomnia)= 0.9 20
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A simple DCE example
➢ Measuring preference under certainty
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Variants of VAS
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Health state description
m
Death
×
Insomnia
×
Full health
×
U(insomnia) = m/10 = 0.40
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VAS-chronic states
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Standard Gamble (SG)
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SG
First presented by von Neumann and Morgenstern in 1944
Classic method based directly on the vNM utility theory
Extensively used in decision analysis Measuring preference under uncertainty
100
% chance
C
0.10 0.90
Full health
Death
CHOICE “B”
100
% chance
Loneliness
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SG - worse than death states
CHOICE “A”
10
% chance
90
% chance
C
0.10 0.90
Full health
1- p Death
MEASUREMENT
UTILITY SCALE
Find p
Assume p=0.8 would risk 20% chance of death to avoid living with insomnia
U (Full health) U (Insomnia)
U (Death)