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VAS, SG, TTO and PTO An Interactive Introduction

VAS, SG, TTO and PTO An Interactive Introduction. 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. Uni-dimensional value.

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VAS, SG, TTO and PTO An Interactive Introduction

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  1. VAS, SG, TTO and PTOAn 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. Normal health X Dead 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 versusworse imaginable health

  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

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