This presentation was part of the workshop at the 6th ISPOR Asia-Pacific Conference intended to educate outcomes researchers on the state of the art of the time trade-off (TTO) procedures for eliciting individuals’ preferences for health outcomes. Workshop W9: Time Trade Off Procedures for Measuring Health State Preferences. See http://ispor.org/Event/ProgramList/2014Beijing?type=Workshop#WorkshopII

1. A Review of the TTO Method for Health State Valuation
Koonal Shah
Office of Health Economics
ISPOR 6thAsia-Pacific Conference • 6-9 September 2014
Beijing

2. •
Methods for valuing health states
•
How does TTO work?
•
Why use TTO?
•
Things to consider when designing a TTO study
Agenda

3. Methods for valuing health states
•
Simple ranking exercise
•
Qualitative discriminant process
Ranking techniques
•
Visual analogue scale
•
Likert scale
Rating techniques
•
Willingness to pay
•
Discrete choice experiment
•
Standard gamble
•
Time trade-off
Choice- based techniques

4. Standard gamble
•
Principle underpinning standard gamble: the worse the health state, the higher the risk of immediate death one will accept in order to avoid it

5. Health state
YEARS
Full health
Dead
t
x
•
Principle underpinning TTO: the worse the health state, the more time in full health one will be willing to sacrifice in order to avoid it
Time trade-off (TTO)
VALUE

6. •
Respondent is presented with a paired comparison
•
The choice is between two hypothetical ‘lives’
•
Unlike the standard gamble, both alternatives involve certain (rather than uncertain) outcomes
How does TTO work?

7. •
For a specified chronic health state preferred to death:
•
Life A involves living for period tin the specified health state
•
Life B involves living in ‘full health’ for period xwhere x< t
•
Time xis varied until the respondent is indifferent between the two lives
•
The score given to the health state is then x/t
How does TTO work? (2)

8. •
Q: Would you rather live for 10years in the health state (Life A) or for 5years in full health (Life B)?
•
A: I prefer Life A
•
Q: Would you rather live for 10years in the health state (Life A) or for 6years in full health (Life B)?
How does TTO work? (3)
If respondent prefers Life A, Life B is made moreattractive
If respondent prefers Life B, Life B is made lessattractive

9. Health state = ?
YEARS
Full health = 1
Dead = 0
t
x
How does TTO work? (4)
VALUE

10. Health state = 0.5
YEARS
Full health = 1
Dead = 0
10
5
How does TTO work? (4)
VALUE
Suppose the respondent is indifferent between living in full health for 5years and living in the health state for 10years
Health state value = x/t= 5/10 = 0.5

11. Health state = 0.9
YEARS
Full health = 1
Dead = 0
10
9
How does TTO work? (4)
VALUE
Suppose the respondent is indifferent between living in full health for 9years and living in the health state for 10years
Health state value = x/t= 9/10 = 0.9

12. •
A key assumption required for the current TTO approach is constant proportionality
•
Requires that respondents are prepared to give up the same proportion of time (e.g. 40%) in full health (x),regardless of the length of time in the health state (t) being considered
•
If a respondent is indifferent between t= 10 years and x= 6 years (resulting in a value of 0.6), they should also be indifferent between t= 5 years and x= 3 years
Constant proportionality

13. •
Involves the concept of choice
•
Developed specifically for use in health care
•
Most people find it easier to think about time than to think about probabilities
•
Respondents only have to consider one health state at a time
Why use TTO?

14. •
Which mode of administration is most suitable?
•
How should health states considered to be worse than dead be valued?
•
What procedure should be used for arriving at the respondent’s point of indifference?
Things to consider when designing a TTO study

15. Please address enquiries to Koonal Shah at kshah@ohe.org
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