A Comparison of Alternative Variants of the Lead and Lag Time TTO

Abstract

Background: The estimation of Quality Adjusted Life Years gained from treatment requires length of life to be quality adjusted by the weight ('value') attached to the quality of life in each health state. These weights are anchored on a scale of 1 for full health and 0 for dead, with health states considered to be so bad that they are worse than being dead, having negative values. A widely used method for obtaining these values is the 'Time Trade Off' (TTO). The National Institute for Health and Clinical Excellence (NICE), for example, recommend the use of TTO values in evidence submitted to it on the cost effectiveness of new technologies. However, there are some important problems with TTO. These problems centre on the inability of the method adequately to handle very poor states of health, which people may consider to be worse than dead. Where that arises, the TTO has to switch to a different questioning process, with corresponding problems for the comparability and interpretation of values in the negative range. In previous research, we tested a new TTO approach, the 'Lead Time TTO', which is capable of producing weights both for states better and worse than dead in a uniform manner. Aims: The aims of this research are (i) to investigate the values generated from Lead Time TTO (LT-TTO) using different combinations of the duration of the health state and the time in full health which participants are asked to consider; as well as varying the order in which these appear (Lag Time TTO); (ii) to gauge if values generated from these methods concur with participants' views as to whether the states are better or worse than dead (iii) to explore a range of methods for handling the preferences of those whose distaste for very poor health states is such that they 'use up' all their lead time. Methods: A sample of 200 members of the general public valued five health states, using two of four variants of the LT-TTO: a lead time of 10 years with a health state duration of 20 years; a lead time of 5 years and a health state duration of 1 year; a lead time of 5 years and a duration of 10 years; and a duration of 5 years with a lag time of 10 years. Participants also responded to a range of supplementary tasks and other questions. Results: Values are influenced by the length of the lead time relative to the health state duration. Longer lead times enable somewhat more preferences to be captured, but appear to exert a framing effect on values. Lag time TTO results in less non-trading for mild states, and to participants trading off less time for severe states. Of those who valued the worst health state as negative, 70% also expressed the view that this state was worse than dead. Conclusions: LT-TTO confers an important advantage over the traditional TTO by providing a single method capable of generating positive and negative values that seem broadly in keeping with participants' stated views about those states being better or worse than dead. However, values are sensitive to the length of time in full health relative to the d...

The effects of lead time and visual aids in TTO valuation: a study of the EQ-VT framework

“…Several possible reasons for the effect of the LT/UT ratio on TTO values were proposed previously [6, 9]. The main reason could be the framing effect of the lead time or total tradable time used.…”

“…This visual error is more likely to affect the valuation of states with mild health problems. The design factor is the iteration process [9], which is another potential influence on values. In this and previous studies, values for states worse than dead were searched in steps proportional to the length of unhealthy time and lead time.…”

“…This recommendation is also supported by the trivial exhaustion of tradable time occurring in the study arm using equal lead time and unhealthy time. Previous studies suggested that exhaustion of tradable time may not be completely eliminated by extending the lead time [6, 9]. One advantage of using equal lead time and unhealthy time in TTO valuation is that the transformation of negative values can be avoided, as the possible range of generated values is −1 to 1.…”

The EuroQol Group after 25 years

“…Reflecting the ongoing priorities of the VTF there were 2 papers on lead time and lag time TTO (Attema et al 2010;Devlin et al 2010) and one on the experimental design and modelling of a hybrid/combination of TTO and DCE. (Oppe and .…”

A Note on the Expected Biases in Conventional Iterative Health State Valuation Protocols

“…On the other hand, untransformed negative values using the TTO board range from -39 to 0, but it is not clear whether respondents fully appreciate this, or how they would react if they did. Furthermore, there is evidence to suggest that the recently developed 'lead-time' version of TTO, which reconciles the inconsistency between the visual aid and implied values in the negative range (32), suffers from its own range bias, where the values are affected by the lowest value that the visual aid accommodates (33).…”