1 VAS, SG, TTO and PTO An Interactive Introduction

2 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

3 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

4 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

5 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

6 Visual Analogue Scale  VAS  Also called “category scaling”  From psychological research  “How is your quality of life?”  “X” marks the spot  Rescale to [0..1]  Different anchor point possible:  Normal health (1.0) versus dead (0.0)  Best imaginable health versus worse imaginable health Dead Normal health X

7 Consistent picture of difference 103 students

8 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