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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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Screen shot of a question in the conventional TTO procedure
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Fig4: Screen shot of a question in the conventional TTO procedure

Mentions: The two TTO procedures were designed to differ only on those elements necessary to perform our test. Appendix 3 graphically illustrates this by presenting screen shots of two questions that a subject may have faced during the experiment, one for the conventional procedure (Fig. 4) and one for the alternative procedure (Fig. 5). Table 1 further clarifies these procedures by presenting the stimuli, an imaginary subject would face for a particular choice pattern in case of the gauge duration nβ = 10 years. The table shows that an indifference value of nγ = 7.5 was stored for this subject. Hence, this value was subsequently used as the gauge duration in the alternative procedure. Procedural invariance would then require the resulting elicited indifference value of nβ to be (approximately) 10 again. Our imaginary subject violates procedural invariance to a small extent, however, resulting in an estimated indifference value of 10.75.Table 1


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)

Screen shot of a question in the conventional TTO procedure
© Copyright Policy
Related In: Results  -  Collection

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

Fig4: Screen shot of a question in the conventional TTO procedure
Mentions: The two TTO procedures were designed to differ only on those elements necessary to perform our test. Appendix 3 graphically illustrates this by presenting screen shots of two questions that a subject may have faced during the experiment, one for the conventional procedure (Fig. 4) and one for the alternative procedure (Fig. 5). Table 1 further clarifies these procedures by presenting the stimuli, an imaginary subject would face for a particular choice pattern in case of the gauge duration nβ = 10 years. The table shows that an indifference value of nγ = 7.5 was stored for this subject. Hence, this value was subsequently used as the gauge duration in the alternative procedure. Procedural invariance would then require the resulting elicited indifference value of nβ to be (approximately) 10 again. Our imaginary subject violates procedural invariance to a small extent, however, resulting in an estimated indifference value of 10.75.Table 1

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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