Transcript Intro QALY & need assessment

VAS, SG, TTO and PTO
An Interactive Introduction
1
Value a health state
 Wheelchair
 Some problems in walking about
 Some problems washing or dressing
 Some problems with performing usual activities
 Some pain or discomfort
 No psychosocial problems
2
Uni-dimensional value
 Like
the IQ-test measures intelligence
 Ratio or interval scale
 Difference 0.00 and 0.80 must be 8 time higher than 0.10
 Three
popular methods have these
pretensions
 Visual analog scale
 Time trade-off
 Standard gamble
3
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)
= .8
4
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 .8
5
Visual Analogue Scale
Normal
health
 VAS
 Also called “category scaling”
 From psychological research
 “How
is your quality of life?”
 “X” marks the spot
X
 Rescale to [0..1]
 Different
anchor point possible:
 Normal health (1.0) versus dead (0.0)
 Best imaginable health versus
worse imaginable health
Dead
6
Consistent picture of difference
Utilities
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
SG
TTO
VAS
103 students
0.2
0.1
0.0
3
33
33
3
23
22
3
32
22
1
32
33
2
23
21
1
21
32
2
12
11
2
11
11
1
12
11
1
11
21
1
21
11
1
11
12
EQ-5D health states
7
Health economics prefer TTO/SG
 Visual
analogue scale
 Easy
 No trade-off: no relation to QALY
• No interval proportions
 Standard
Gamble / Time trade-Off
 Less easy
 Trade-off: clear relation to QALY
• Interval proportions
 Little
difference between SG and TTO
8