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Impacts of Food Hypersensitivities on Quality of Life in the UK and Willingness to Pay (WTP) to remove those impacts

Appendix O: Protest Votes, Task Difficulty and Debriefs on DCE and BWS

The DCE training choice sets included removal of the FHS, for durations up to 20 years, at zero cost.

If people declined free removal in all 3 training sets (ie including the removal of FHS for 20 years for free) they were skipped past the priced DCE – since they had declined the ‘best’ offer (20 years) at zero price.

People who always chose to buy the pill in the 9 sets were presented with debrief questions to allow identification of protest or problematic behaviour – for example people not taking the price seriously. Likewise, people who never chose to buy the pill in the 9 sets, in this case problematic responses included not thinking that the pill would be safe and therefore not considering buying it.

Everyone who completed the 9 priced choice sets were asked debrief questions on

  • how hard it was to understand the DCE choices
  • how hard it was to make the DCE choices.

DCE Adults

Declining 3 zero price options: Adults

53% accepted the free removal in all 3 choice sets, but 16% declined removal of their FHS in one choice set and 11% rejected free removal in all 3 training sets, one of which was for a duration of 20 years.

Table 1: Number of Free Options Declined

Number of options Frequency Percent Cumulative
0 754 52.88 52.88
1 222 15.57 68.44
2 289 20.27 88.71
3 161 11.29 100.00
Total 1426 100.00 -

The finding that 11% of adults with a FHS would not accept its removal for 20 years at zero cost was not anticipated at the start of the research process. The issue of adjustment costs had featured in the focus groups which had prompted the researchers to increase the maximum duration used in the zero price DCE training sets to 20 years – to identify people who would never buy in the priced DCE sets.

Figure 1. Number of zero price removals of FHS declined, adults.

Details explained in the text.

The 161 people declining all 3 free removals were excluded from the priced DCE experiment. This group were asked what was the minimum duration (if any) that they would accept for unpriced removal of their FHS condition. 

Table 2: What is the minimum period that would induce you to accept free removal?

Period of time Frequency Percent Cumulative
25 years 3 1.86 1.86
35 years 4 2.48 4.35
40 years 4 2.48 6.83
45 years 1 0.62 7.45
50 years 4 2.48 9.94
Permanent removal only 88 54.66 64.60
Decline removal 57 35.40 100.00
Total 161 100.00 -

Of the 161 people who always rejected free removal, 10% would choose removal if it was for a longer, but still temporary, period, 55% would only accept permanent removal and 35% (57 people) did not want their FHS removed at all.

Protest Choices: Adults

People who had accepted the free removal but who never bought the pill in any of the 9 choice sets that followed were directed to a question asking why that was. This was in part to distinguish potential buyers who could be included in the DCE analysis (ie potential buyers who could not afford the prices shown) from people who rejected the premise of the choice tasks, would never buy and should be excluded from the DCE analysis.

Table 3: Why did you never pay for the pill?

Reason for not paying Frequency Percent Cumulative
Cost too high for benefit 149 36.79 36.79
I did not trust it's safety 9 2.22 39.01
I did not trust it would work 10 2.47 41.48

I could not afford what was asked

124 30.62 72.10
Removal length was not worthwhile 34 8.40 80.49
The government should pay 37 9.14 89.63
Other 42 10.37 100.00
Total 405 100.00 -

Responses in bold (the pill regarded as not safe, or ineffective, or a view that the government should pay) were treated as indicating rejection of the valuation process and excluded from the choice models estimated on the DCE data.

People who always bought the pill in all 9 choice sets were directed to a question asking why that was. 

Table 4: Why did you always pay for the pill?

Reasons for not paying Frequency Percent Cumulative
Prices unrealistic so ignored 7 10.77 10.77
The cost was small compared to benefit 46 70.77 81.54
Other 12 18.46 100.00
Total 65 100.00 -

Ignoring the price was regarded as a rejection of the valuation process and people citing that as a reason for always ‘buying’ were excluded from the choice models estimated on the DCE data.

A total of (56 + 7) 63 people who completed the priced DCE were therefore excluded from the analysis, this is less than 4.5%.

DCE Debriefs: Adults

Aggregating across the three conditions 88% of the adult sample regarded the DCE as “easy” or “very easy” to understand and less than 10% of the sample regarded the DCE as “difficult” or “very difficult”.

Table 5. How easy was it to understand the WTP questions? – Full Sample

Understand scale Frequency Percent Cumulative
Very difficult 14 1.11 1.11
Difficult 99 7.83 8.93
No opinion 85 6.72 15.65
Easy 561 44.35 60.00
Very easy 506 40.00 100.00
Total 1265 100.00 -

The pattern was consistent across the FHS conditions, as shown in Figure 2. 

Figure 2: Ease of understanding DCE choices, adults

Details explained in the text.

A separate question was regarding the difficulty of making the DCE choices. Fewer than 3.5% of the sample found making the DCE choices “very difficult” but about a quarter did find them difficult. This response pattern is not in itself a cause of concern, in fact researchers want people to have to exert to make their choices as it suggests respondents are considering the tradeoffs when making their choices, and that the attribute levels are such that tradeoffs have to be considered carefully when making choices. For example, if the prices were excessively low then people would find the choices ‘easy’, but the price term would likely be insignificant and WTP estimates not retrievable).

Table 6: How easy was it to decide your responses to the WTP questions? Full sample

Understand scale Frequency Percent Cumulative
Very difficult 41 3.24 3.24
Difficult 305 24.11 27.35
No opinion 77 6.09 33.44
Easy 556 43.95 77.39
Very easy 286 22.61 100.00
Total 1265 100.00 -

The pattern is similar when disaggregated by condition, as shown in Figure 3.   The percentage reporting the choices as “very difficult” ranged between 1.6% and 4.1%.  The proportion reporting the choices as “easy” or “very easy” ranged from 62% (allergy) to 73% (coeliac disease).

Figure 3. Ease of making DCE choices, adults. 

Details explained in the text.

DCE: Children

Declining 3 zero price options: Children

If people declined the unpriced removal of their FHS in all 3 choice sets, even for the longest period of 20 years, they were not presented with the priced choice sets which are the basis of the WTP analysis presented below. 

In the Parent sample 18% declined removal of their child’s FHS in one choice set, 26% declined removal of their FHS in two choice sets and 17% of respondents declined all 3 free removal options. The probability of declining the free removal declines as the duration increases.

Table 7.  Number of Free Options Declined

Number of options Frequency Percent Cumulative
0 277 38.69 38.69
1 129 18.02 56.70
2 188 26.26 82.96
3 122 17.04 100.00
Total 716 100.00 -

Figure 4. Number of zero price removals of FHS declined, children

Details explained in the text.

Those who declined all three free removal options were asked the minimum period of removal of their child’s FHS which would induce them to opt for removal.   

Of the 122 people who always rejected free removal in the training sets, one fifth specified a period of temporary removal they would accept, 65% indicated they would only accept permanent removal and 15% (18 people) did not want their child’s FHS removed at all.

Table 8. What is the minimum period that would induce you to accept free removal?
 

Number of years Frequency Percent Cumulative
25 years 10 8.20 8.20
30 years 4 3.28 11.48
35 years 3 2.46 13.93
40 years 3 2.46 16.39
50 years 5 4.10 20.49
Permanent removal only 79 64.75 85.25
Decline removal 18 14.75 100.00
Total 122 100.00 -

Protest Choices: Children

People who never bought the pill in any of the 9 choice sets were directed to a question asking why that was. This was in part to distinguish potential buyers who could be included in the DCE analysis (for example, potential buyers who could not afford the prices shown) from people who rejected the premise of the choice tasks, would never buy and should be excluded from the DCE analysis.

Table 9. Why did you never pay for the pill? 

Reasons for not paying for the pill Frequency Percent Cumulative
Cost too high for benefit 19 21.59 21.59
I could not afford what was asked 26 29.55 51.14
Removal length was not worthwhile 5 5.68 56.82
My child would have to re adjust 22 25.00 81.82
I did not trust it's safety 2 2.27 84.09
I did not trust it would work 1 1.14 85.23
The government should pay 7 7.95 93.18
Other 6 6.82 100.00
Total 88 100.00 -

Responses in bold (the pill regarded as not safe, or ineffective, or a view that the government should pay) were treated as indicating rejection of the valuation process and excluded from the choice models estimated on the DCE data.

People who always bought the pill in all 9 choice sets were directed to a question asking why that was. 

Table 10. Why did you always pay for the pill?

Reasons for always paying for the pill Frequency  Percent Cumulative
Prices unrealistic so ignored 7 10.77 10.77
The cost was small compared to benefit 46 70.77 81.54
Other 12 18.46 100.00
Total 65 100.00 -

Ignoring the price was regarded as a rejection of the valuation process and people citing that as a reason for always ‘buying’ were excluded from the choice models estimated on the DCE data.

A total of (10 + 7) 17 parents who completed the priced DCE were therefore excluded from the analysis, this is less than 3%.

DCE Debriefs: Children

Aggregating across the three conditions 70% of the adult sample regarded the DCE as “easy” or “very easy” to understand and less than 4% of the sample regarded the DCE as “very difficult”.

Table 11: How easy was it to understand the WTP questions? Full sample

Understand scale Frequency Percent Cumulative
Very difficult 23 3.87 3.87
Difficult 86 14.48 18.35
No opinion 67 11.28 29.63
Easy 265 44.61 74.24
Very easy 153 25.76 100.00
Total 594 100.00 -

The pattern was consistent across the FHS conditions, as shown in Figure 5. 

Figure 5: Easy of understanding DCE choices, children

Details explained in the text.

A separate question was regarding the difficulty of making the DCE choices. 11% of the sample found making the DCE choices “very difficult” and a third found them difficult. 

As discussed regarding Adult sample, this response pattern is not in itself a cause of concern.

Table 12. How easy was it to decide your response to the WTP questions? – Full Sample

Easy to decide Frequency Percent Cumulative
Very difficult 66 11.11 11.11
Difficult 195 32.83 43.94
No opinion 52 8.75 52.69
Easy 195 32.83 85.52
Very easy 86 14.48 100.00
Total 594 100.00 -

The pattern is similar when disaggregated by condition, as shown in Figure 6. 

Figure 6. Ease of making DCE choices, children. 

Details explained in the text.

BWS Debriefs

The BWS tasks were completed only by adults, not by parents (in part because the components of the child FIQLQ and FAQLQ instruments vary by child age and so a single BWS design was not possible for the Parent survey). It is the debrief data from the adults that is presented here. 

Understanding the BWS Choices.

Figure 7. Ease of understanding BWS allergy choices, adults.

Details explained in the text.

Table 13: BWS understanding Food Allergy

Easy to decide Frequency Percent Cumulative
Very difficult 12 3.12 3.12
Difficult 38 9.87 12.99
No opinion 48 12.47 25.45
Easy 176 45.71 71.17
Very easy 111 28.83 100.00
Total 385 100.00 -

Figure 8. Ease of understanding BWS coeliac disease choices, adults.

Details explained in the text.

Table 14: BWS understanding Coeliac disease

 

BWS choice difficulty Frequency Percent Cumulative
Very difficult 8 1.33 1.33
Difficult 73 12.15 13.48
No opinion 102 16.97 30.45
Easy 282 46.92 77.37
Very easy 136 22.63 100.00
Total 601 100.00 -

Figure 9: Ease of understanding BWS intolerance choices, adults

Tables explain the data in full.

Table 15: BWS understanding Food intolerance

 

BWS choice difficulty Frequency Percent Cumulative
Very difficult 8 1.82 1.82
Difficult 64 14.55 16.36
No opinion 53 12.05 28.41
Easy 202 45.91 74.32
Very easy 113 25.68 100.00
Total 440 100.00 -

Making the BWS Choices

Figure 10: Ease of making BWS allergy choices, adults

Details explained in the text.

Table 16: BWS choice difficulty Food Allergy

BWS choice difficulty Frequency Percent Cumulative
Very difficult 25 6.49 6.49
Difficult 124 32.21 38.70
No opinion 37 9.61 48.31
Easy 138 35.84 84.16
Very easy 61 15.84 100.00
Total 385 100.00 -

Figure 11: Ease of making BWS coeliac disease choices, adults

Details explained in the text.

Table 17: BWS choice difficulty: coeliac disease

BWS choice difficulty Frequency Percent Cumulative
Very difficult 22 3.66 3.66
Difficult 206 34.28 37.94
No opinion 86 14.31 52.25
Easy 228 37.94 90.18
Very easy 59 9.82 100.00
Total 601 100.00 -

Figure 12: Ease of making BWS intolerance choices, adults

Details explained in the text.

Table 18: BWS choice difficulty: Food intolerance

BWS choice difficulty Frequency Percent Cumulative
Very difficult 16 3.64 3.64
Difficult 133 30.23 33.86
No opinion 50 11.36 45.23
Easy 179 40.68 85.91
Very easy 62 14.09 100.00
Total 440 100.00 -

Summary

The survey was characterised by low levels of protest behaviour in the price DCE, although significant numbers were not included in the priced DCE because of their rejection of the 20-year removal at zero cost in the training choice sets.

The extent to which people found the DCE choice sets easy to understand was regarded as a positive finding. Finding those choices difficult to make was a more common occurrence, but was not regarded as problematic, given the feedback from the focus groups and the statistic results derived from the choice data.

A similar pattern was observed for the BWS choice sets – making the choices was harder than understanding the choice required.