Time Trade-Off (TTO)

The Time Trade-Off (TTO) method is a choice-based technique used to elicit health state utility values, reflecting the length of remaining life expectancy that an individual may be willing to trade to avoid living in a less-than-perfect health state. The TTO method helps quantify the perceived quality of different health states by asking respondents to make trade-offs between longevity and health quality.

Key aspects of the Time Trade-Off method include:

– Concept: Respondents are asked to consider remaining in a specified health state (Health State A) for a given period (typically 10 years) and then dying without pain. They are then asked how many years they would need to live in full health (and then dying without pain) to make this option equally desirable as being in Health State A for 10 years.

– Utility Calculation: The utility value of Health State A is determined by the number of years in full health that the respondent equates to 10 years in Health State A. For example, if the respondent considers 8 years in full health as equivalent to 10 years in Health State A, Health State A is assigned a utility value of 0.8 (80% of full health).

– QALY Calculation: Both options would then provide 8 quality-adjusted life years (QALYs), calculated by multiplying the number of years by the utility value (10 years × 0.8 utility = 8 QALYs).

– Discounting Future Health: A limitation of the TTO method is that people may value health in future years differently from health at the current time. To account for this, discount rates are applied to QALYs in economic evaluations to adjust the value of future health benefits. However, since it is impossible to determine the exact discount rate for each individual, the adjustments may not perfectly reflect true preferences.

– Limitations: The TTO method assumes that respondents can accurately envision and compare different health states and their durations, which may not always be the case. Additionally, personal preferences and the subjective nature of health perceptions can introduce variability in the responses.


A respondent is asked to choose between living in a specific health state (Health State A) for the next 10 years or living in full health for a shorter period before dying without pain. If the respondent indicates that living 8 years in full health is as desirable as living 10 years in Health State A, the utility value of Health State A is calculated as 0.8.

The Time Trade-Off method is widely used in health economics to derive utility values for different health states, providing essential data for calculating QALYs in cost-utility analyses. Despite its limitations, the TTO method offers a valuable approach to understanding how individuals value different aspects of their health and longevity.