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The way that you do it? An elaborate test of procedural invariance of TTO, using a choice-based design.

Attema AE, Brouwer WB - Eur J Health Econ (2011)

Bottom Line: An important problem with this method is that results have been found to be responsive to the procedure used to elicit preferences.We find no violations of procedural invariance except for the shortest gauge duration.The results for CPTO are more troublesome: TTO scores depend on gauge duration, reinforcing the evidence reported when using the conventional procedure.

View Article: PubMed Central - PubMed

Affiliation: iBMG/iMTA, Erasmus University, PO Box 1738, 3000, DR, Rotterdam, The Netherlands. attema@bmg.eur.nl

ABSTRACT
The time tradeoff (TTO) method is often used to derive Quality-Adjusted Life Year health state valuations. An important problem with this method is that results have been found to be responsive to the procedure used to elicit preferences. In particular, fixing the duration in the health state to be valued and inferring the duration in full health that renders an individual indifferent, causes valuations to be higher than when the duration in full health is fixed and the duration in the health state to be valued is elicited. This paper presents a new test of procedural invariance for a broad range of time horizons, while using a choice-based design and adjusting for discounting. As one of the known problems with the conventional procedure is the violation of constant proportional tradeoffs (CPTO), we also investigate CPTO for the alternative TTO procedure. Our findings concerning procedural invariance are rather supportive for the TTO procedure. We find no violations of procedural invariance except for the shortest gauge duration. The results for CPTO are more troublesome: TTO scores depend on gauge duration, reinforcing the evidence reported when using the conventional procedure.

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Relation between gauge duration and unadjusted TTO scores (alternative procedure). The gauge duration was the answer given by the subject to the corresponding question in the conventional procedure. Because these answers obviously differed between subjects, we use a scatter plot here
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Fig3: Relation between gauge duration and unadjusted TTO scores (alternative procedure). The gauge duration was the answer given by the subject to the corresponding question in the conventional procedure. Because these answers obviously differed between subjects, we use a scatter plot here

Mentions: Next, we investigated CPTO for the alternative procedure. Figures 1 and 2 already indicated that TTO scores were not independent from gauge duration. The Friedman test of equal TTO scores for all five durations in the alternative procedure confirmed this; it was rejected for both unadjusted and adjusted TTO scores (P < 0.01). The unadjusted TTO scores increased (at a decreasing rate) with duration until 31 years and decreased slightly between 31 and 46 years, i.e., we found a predominantly positive correlation, as shown in more detail in Fig. 3. The same finding held for adjusted scores, although the gap between unadjusted and adjusted scores increased with duration, and the variance was reduced throughout when we adjusted for discounting. Notice the considerable amount of heterogeneity between subjects. This is hard to explain, considering the homogeneity of the sample. One possibility is that young people, having little or no experience with the presented health state, have different interpretations of the seriousness of this scenario. Another possibility is that subjects have difficulty imagining small life expectancies, especially when faced with the shortest gauge durations.Fig. 3


The way that you do it? An elaborate test of procedural invariance of TTO, using a choice-based design.

Attema AE, Brouwer WB - Eur J Health Econ (2011)

Relation between gauge duration and unadjusted TTO scores (alternative procedure). The gauge duration was the answer given by the subject to the corresponding question in the conventional procedure. Because these answers obviously differed between subjects, we use a scatter plot here
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3375425&req=5

Fig3: Relation between gauge duration and unadjusted TTO scores (alternative procedure). The gauge duration was the answer given by the subject to the corresponding question in the conventional procedure. Because these answers obviously differed between subjects, we use a scatter plot here
Mentions: Next, we investigated CPTO for the alternative procedure. Figures 1 and 2 already indicated that TTO scores were not independent from gauge duration. The Friedman test of equal TTO scores for all five durations in the alternative procedure confirmed this; it was rejected for both unadjusted and adjusted TTO scores (P < 0.01). The unadjusted TTO scores increased (at a decreasing rate) with duration until 31 years and decreased slightly between 31 and 46 years, i.e., we found a predominantly positive correlation, as shown in more detail in Fig. 3. The same finding held for adjusted scores, although the gap between unadjusted and adjusted scores increased with duration, and the variance was reduced throughout when we adjusted for discounting. Notice the considerable amount of heterogeneity between subjects. This is hard to explain, considering the homogeneity of the sample. One possibility is that young people, having little or no experience with the presented health state, have different interpretations of the seriousness of this scenario. Another possibility is that subjects have difficulty imagining small life expectancies, especially when faced with the shortest gauge durations.Fig. 3

Bottom Line: An important problem with this method is that results have been found to be responsive to the procedure used to elicit preferences.We find no violations of procedural invariance except for the shortest gauge duration.The results for CPTO are more troublesome: TTO scores depend on gauge duration, reinforcing the evidence reported when using the conventional procedure.

View Article: PubMed Central - PubMed

Affiliation: iBMG/iMTA, Erasmus University, PO Box 1738, 3000, DR, Rotterdam, The Netherlands. attema@bmg.eur.nl

ABSTRACT
The time tradeoff (TTO) method is often used to derive Quality-Adjusted Life Year health state valuations. An important problem with this method is that results have been found to be responsive to the procedure used to elicit preferences. In particular, fixing the duration in the health state to be valued and inferring the duration in full health that renders an individual indifferent, causes valuations to be higher than when the duration in full health is fixed and the duration in the health state to be valued is elicited. This paper presents a new test of procedural invariance for a broad range of time horizons, while using a choice-based design and adjusting for discounting. As one of the known problems with the conventional procedure is the violation of constant proportional tradeoffs (CPTO), we also investigate CPTO for the alternative TTO procedure. Our findings concerning procedural invariance are rather supportive for the TTO procedure. We find no violations of procedural invariance except for the shortest gauge duration. The results for CPTO are more troublesome: TTO scores depend on gauge duration, reinforcing the evidence reported when using the conventional procedure.

Show MeSH