APPENDIX 1: Choice scenarios, levels of risk and expected QALY gains
Scenario / Health state 1 / Health state 2 / Level of risk / Expected QALY gain*Q1 / Q2
1 / 22222 / 11131 / 10% / 0.021 / 0.0105
2 / 33232 / 33323 / 50% / 0.009 / 0.0045
3 / 21312 / 12111 / 2% / 0.011 / 0.0055
4 / 22323 / 21312 / 2% / 0.0074 / 0.0037
5 / 22323 / 12111 / 2% / 0.015 / 0.0075
6 / 21232 / 32211 / 4% / 0.0092 / 0.0046
7 / 11112 / 22121 / 10% / 0.008 / 0.004
8 / 11122 / 22122 / 10% / 0.012 / 0.006
9 / 21323 / 22233 / 4% / 0.012 / 0.006
10 / 22331 / 21133 / 4% / 0.0075 / 0.00375
11 / 21111 / 12121 / 50% / 0.066 / 0.033
12 / 23232 / 32232 / 50% / 0.028 / 0.014
13 / 11312 / 11113 / 10% / 0.0144 / 0.0072
14 / 12311 / 11211 / 2% / 0.0068 / 0.0034
15 / 32311 / 12311 / 10% / 0.0161 / 0.008
16 / 32311 / 11211 / 2% / 0.01 / 0.005
17 / 21111 / 12211 / 50% / 0.039 / 0.0195
18 / 32313 / 32331 / 50% / 0.002 / 0.001
19 / 11211 / 22211 / 4% / 0.0047 / 0.0024
20 / 23313 / 11133 / 50% / 0.042 / 0.021
21 / 11121 / 22112 / 10% / 0.021 / 0.0105
22 / 12223 / 13332 / 10% / 0.014 / 0.007
23 / 11312 / 11211 / 2% / 0.0077 / 0.0039
24 / 11332 / 11312 / 4% / 0.0132 / 0.0066
25 / 11332 / 11211 / 2% / 0.0142 / 0.0071
26 / 21222 / 33321 / 2% / 0.0082 / 0.0041
27 / 22222 / 13311 / 50% / 0.0415 / 0.0208
28 / 11112 / 22112 / 4% / 0.0047 / 0.0024
29 / 33212 / 32223 / 4% / 0.0087 / 0.0044
* Risk reduction to zero in Q1, halved in Q2.
APPENDIX 2: Example of the graphical explanation of the concept of risk (screenshot from the questionnaire)[1]
The procedure: A 10 by 10 matrix of green dots was used to represent a hundred people. An accompanying textbox explained that each dot represented an individual “just like you”. To demonstrate the meaning of, for example, a 40% chance of becoming ill, we asked respondents to click on one of the green dots (by clicking the selected dot was marked with an ‘X’). Respondents were then told that the computer would randomly select 40 of the hundred dots and turn them red, and that the chance that the dot they marked would turn red therefore was 40 in 100, or 40%. The same example was repeated with the probability of 1%.
APPENDIX 3: Scenario descriptions of WTP questions
Q1 / Suppose that you are in the health state that you assessed as the better one. However, you face the risk of moving to the worse health state tomorrow. If this happens, you will remain in the worse health state for the duration of one year. After this year, you will return to the better health state.The risk you face that this will happen tomorrow is 10%. This means that you have a 10 in 100 chance of moving to the worse state and a 90 in 100 chance of remaining in the better state.
You can avoid this risk of health loss completely by taking a medicine (with no side effects) each month. You will then certainly remain in the better health state. You must pay for this medicine yourself, from your (family) income.
Q2 / Suppose that you are in the health state that you assessed as the better one. However, you face the risk of moving to the worse health state tomorrow. If this happens, you will remain in the worse health state for the duration of one year. After this year, you will return to the better health state.
The risk you face that this will happen tomorrow is 10%. This means that you have a 10 in 100 chance of moving to the worse state and a 90 in 100 chance of remaining in the better state.
You can reduce this risk of health loss by taking a medicine (with no side effects) each month. As a result, your risk of moving to the worse health state will be halved from 10% to 5%. You must pay for this medicine yourself, from your (family) income.
Appendix 4: Example of the payment scale used (screenshot from the questionnaire)
[1] Exact translation from Dutch: “Now imagine that in this group of 100 people the probability that someone becomes ill rises to 40%. In other words, 40 people will become ill and 60 people will not. To get an idea of what it means for the probability that you will be one of the people becoming ill, choose a green dot and click on it. The probability of the dot you selected changing colour is 40 to 100.”