Evaluating discrete choice experiment willingness to pay [DCE-WTP] analysis and relative social willingness to pay [RS-WTP] analysis in a health technology assessment of a treatment for an ultra-rare childhood disease [CLN2]

Figures & data

Figure 1. Example DCE-WTP preamble and question.

Table 1. Details of DCE-WTP instrument attributes and levels

Attribute	Levels
Additional income tax (hypothecated for CLN2)	Levels of £0, £25, £50, or £100.
Increase in life expectancy as a consequence of treatment	Levels of 0, 2, 5, 10, 15, or 20 years.
Quality of life of affected child at treatment initiation	- Levels of: - Not affected - Badly controlled seizures - Frequent seizures - Controllable seizures
Treatment effect on child’s capabilities	- Levels of: - No effect - Yes—Slow down - Yes—Remain - Yes—Improved

Figure 2. Example RS-WTP preamble and question.

Figure 2. Continued.

Table 2. Details of RS-WTP instrument attributes and levels

Attribute	Levels
Increase in life expectancy as a consequence of treatment	- Levels of 0, 5, 10, or 20 years
Quality of life of affected child at treatment initiation	- Levels of: - Not affected - Badly controlled seizures - Frequent seizures - Controllable seizures
Treatment effect on child’s capabilities	- Levels of: - No effect - Yes—Slow down - Yes—Remain - Yes—Improved

Table 3. Estimates of MWTP in £s—Whole sample using Random Parameter Logit including all responses except ‘unwilling to choose’ responses but including ‘indifference’ responses. Non-linear model using squared root of child life expectancy

Dependent variable.	Marginal Willingness to Pay [MWTP].	P>[z].	95% CI.	95% CI.
Child life expectancy square root.	£32/Square root of number of years of additional life expectancy.	<0.01
Quality of Life (compared to the base category of ‘Badly controlled seizures’)
Not Affected.	£187	<0.01	£166	£208
Controllable seizures.	£123	<0.01	£109	£137
Frequent Seizures.	£76	<0.01	£65	£86
Treatment effect (compared to the base category of ‘No effect’)
Slowdown.	£125	<0.01	£111	£139
Remain.	£149	<0.01	£132	£166
Improved.	£185	<0.01	£165	£205

Figure 3.. Non-linear decrease in MWTP in £5 for an additional life year with respect to life expectancy.

Table 4. RS-WTP Econometric results—WTP in £s for Service 1 (Imperfect Health)—Linear OLSContinuous Life Expectancy

Variable	Implied Percentage (%) of the budget/Estimated coefficient	Standard Error	Pr (>[t])	95% CI	95% CI
Intercept (constant) %	40.11%			39.08%	41.13%
Intercept (constant)	(£8,022)	104.500	<0.01	(£7,817)	(£8,227)
Child Life Expectancy – %	0.15%			0.10%	0.20%
Child Life Expectancy	(£30)	4.850	<0.01	(£21)	(£40)
Quality of Life
Not affected – %	5.60%			4.61%	6.61%
Not affected	(£1,121)	101.778	<0.01	(£922)	(£1,321)
Controllable Seizures – %	3.83%			2.83%	4.83%
Controllable Seizures	(£766)	101.778	<0.01	(£567)	(£966)
Frequent Seizures – %	1.42%			0.42%	2.41%
Frequent Seizures	(£284)	101.471	<0.01	(£85)	(£482)
Treatment Effect
Slowdown – %	1.84%			0.85%	2.84%
Slowdown	(£369)	101.622	<0.01	(£170)	(£569)
Remain – %	2.40%			1.41%	3.40%
Remain	(£481)	101.620	<0.01	(£282)	(£680)
Improved – %	2.79%			1.80%	3.78%
Improved	(£558)	101.467	<0.01	(£360)	(£757)
AIC	653,431
BIC	653,506
Pseudo – Log -Likelihood	−326,706

Table 4 footnote: The absolute regression estimates and confidence intervals in () within this table are a by-product of assuming a small £20,000 budget available for allocation. Since there is also evidence to suggest (Richardson et al 2014) that the value of coefficients may be linearly related to the size of the initial arbitrary budget allocation, the implied percentage figures are therefore arguably of more relevance.

Data availability statement

As the underlying preference data cannot be utilized without elaborate econometric modeling, and without providing considerable time-consuming explanations of the data, the underlying data supporting this analysis is not being made publicly available alongside this publication.

However, in principle if peer reviewers or others request access to the data within 2 years of the date of first publication, then we may be prepared to facilitate access to data relating to the actual RS-WTP or DCE-WTP analyses, which are outlined in detail within this paper. Any requested disclosures that we could facilitate, must, however, be in line with any relevant legislation relating to data protection (e.g. including the United Kingdom General Data Protection Act 2018).