Appendix 1: Technical Details of the Time Trade-Off (TTO) Methods
The Conventional Method
In a conventional TTO exercise, respondents are offered a choice between two alternative health states at a time—one is the less desirable health state (hi) and the other is the perfect health state. The time spent in health state hi is fixed at t whereas the length of time (between 0 and t) spent in the perfect health state varies, and both are followed by death. Respondents are asked to imagine themselves in both of the scenarios and find a point (time x) that they are indifferent to the lengths of time spent in health state hi (t) and perfect health (x). The same process is done for each health state to be valued in the study. The utility value of each health state (hi) is then calculated as: \( h_{\text{i}} = x/t. \)
The Chained Method
The chained TTO comprises two stages: in the first stage, participants are asked to compare the temporary health states with the anchor state. The anchor state must be worse than the temporary health state, but better than death. Time spent in the temporary state is fixed at t whereas the time period of the anchor state is varied, both followed by a return to perfect health. Participants are asked to imagine themselves in both of the scenarios and find a time point (X1) between 0 and t for the anchor state where they are indifferent to being in either of the two scenarios. In the second stage, the anchor state will be valued in a conventional TTO exercise where participants are asked to compare the anchor state and a perfect health state. The time period in the perfect health state is varied between 0 and t whereas the anchor state is fixed at t, both followed by death. Participants are asked to imagine themselves in both of the scenarios and find a time point (X2) between 0 and t for the perfect health state where they are indifferent in being in either of the two scenarios. The utilities of the temporary health states being valued will be calculated based on X1 and X2.
The utility value for each of the health profiles developed are calculated as follows, where hi is the utility value for the temporary health states and hj is the utility value for the anchor state.
$$ h_{\text{i}} = 1 - \left( {1 - h_{\text{j}} } \right)\frac{{x_{1} }}{t} $$
$$ h_{\text{j}} = \frac{{x_{2} }}{t}. $$
Combining the above, the formula for calculating the utility value for each of the health profiles is:
$$ h_{\text{i}} = 1 - \left( {1 - \frac{{X_{2} }}{t}} \right)\frac{{X_{1} }}{t}. $$
Appendix 2: Health State Profiles Used in the Study
Control Intervention: Urethrotomy Health State Profiles
Urethrotomy: Mild
Discomfort in the penis and bladder from using a catheter for a few days
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Brief discomfort on passing urine after the catheter is removed
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A few drops of blood after you have finished passing urine
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Mild urinary tract infection giving you mild fever-like symptoms
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Urethrotomy: Moderate
Discomfort in the penis and bladder from using a catheter for a few days
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Discomfort on passing urine after the catheter is removed
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Moderate urethral bleeding which requires you to keep the catheter in longer or have a telescopic examination under anaesthetic
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Serious urinary tract infection which makes you feel ill and requires you to stay in hospital overnight for antibiotics from an IV drip
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Urethrotomy: Severe
Discomfort in the penis and bladder from using a catheter
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Severe urethral bleeding which requires you to have a telescopic examination under anaesthetic
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Serious urinary tract infection which makes you feel ill and requires you to stay in hospital overnight for antibiotics from an IV drip
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Severe pain in the penis and bladder area requiring you to take regular painkillers
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Difficulty getting and maintaining a penile erection for sex
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Experimental Intervention: Urethroplasty Health-State Profiles
Urethroplasty: Mild
Discomfort in the penis and bladder from using a catheter
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Mild mouth pain or discomfort when you eat or drink
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Mild urinary tract infection giving you mild fever-like symptoms
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Mild swelling and wound pain in the area between the testes and back passage
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Urethroplasty: Moderate
Discomfort in the penis and bladder from using a catheter
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Moderate and constant mouth pain and scarring in the mouth needing regular painkillers
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Serious urinary tract and wound infection which makes you feel ill and requires you to stay in hospital overnight for antibiotics from an IV drip
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Moderate wound pain in the area between the testes and back passage needing regular painkillers
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Urethroplasty: Severe
Discomfort in the penis and bladder from using a catheter
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Severe and constant mouth pain and scarring in the mouth needing regular painkillers
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Serious urinary tract and wound infection which makes you feel ill and requires you to stay in hospital overnight for antibiotics from an IV drip
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Severe wound pain in the area between the testes and back passage needing regular painkillers
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Leakage of urine from the area between the testes and back passage requiring you to wear incontinence pads
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Difficulty getting and maintaining a penile erection for sex
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Anchor State
Severe pain state
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You have recently been injured and as a result of the injury:
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You are able to do basic tasks (e.g. washing, feeding and communicating) but you have problems walking about
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You have extreme pain and discomfort. No medication can completely alleviate the pain
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You cannot take part in usual activities (e.g. work, social activities and exercise)
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Appendix 3: TTO Interview Scripts and Instructions
Conventional TTO interview script (underline) and instructions
Introduction
Interviewer introduce oneself and thank the participant for their time. Indicate that it is expected to spend up to 1 hour on this interview. Ask the participant if they have any questions before the interview begins. Take written consent from the participant.
Ask the participant to fill in the consent form and the ‘TTO Study—Data Collection Form’. Let the participant know that the data collection form is just to provide details which will help with the analysis later on. All details will be kept anonymous and confidential.
Reiterate that the interview is voluntary and can finish at any time that they wish.
Format and Purpose of the interview
The interview we will be doing today is a little different to any interview you may have done before, but don’t worry we will explain everything fully as we go along and run through a practice at the beginning to make sure you are comfortable with the task. What we will be doing today is an activity called a time trade off exercise which is a tool used by health economists to put a number on how you value a particular state of health. We are going to use this board [point at the TTO board] throughout the interview and each of these cards is going to describe and represent a particular state of health. I will call these cards health states. We are going to ask you to imagine yourself in these health states and think about how you may feel in a situation where your heath is as it is described on the card. We are now going to do a practice run to help you understand how the interview works. There are no right or wrong answers in this practice session.
Practice Exercise
I am first going to show you three health states. These are just general health states and do not bear any reflection on your actual health at the moment. I would like you to imagine how you might feel and be affected if your health was as described on each card.
Ask the participant to read the ‘practice profiles’ out loud and ask them to rank the health states from the best to the worst state. Remind the participant that this is not ‘most like their health’ but is simply the best to worst at face value of each card. Write down the order chosen by the participant (they are labelled on the back of the card A–C).
Describe the task: On the board there are two lives A and B. ‘Life A’ is going to last for 14 days—this won’t change during the interview. The other health state or ‘Life B’ will vary in how long it lasts—up to a maximum of 14 days.
Place one of the practice cards opposite the marker for ‘Life A’. In Life A you should imagine that your health is as described in this health state. You will be in that health state for 14 days then at the end of the 14 days you will die a quick and painless death.
Place the ‘perfect health’ card opposite the marker for ‘Life B’. In Life B you will have perfect health. The length of time you spend in this health state will vary throughout the interview but same as in Life A, at the end of time in this health state, you will die a quick and painless death.
Ask the participant to read these health states again and to try to imagine themselves in these health states.
Move both markers to 14 days and ask the participant the following question: Would you prefer ‘Life B’, perfect health, for 14 days followed by a quick and painless death or would you prefer ‘Life A’ for 14 days followed by a quick and painless death?
Presumably, the participant will make the logical decision to choose Life B. Therefore, move the marker next to ‘Life B’ to 1 day and ask the participant the following question: Would you prefer 1 day in ‘Life B’ followed by a quick and painless death or would you prefer ‘Life A’ for 14 days followed by a quick and painless death? Or would you not be able to choose between the two?
Continue asking this question for the scenario where ‘Life B’ lasts for 13 days, 2 days, 12 days, 3 days, 11 days, 4 days, 10 days, 5 days, etc. until the participant cannot decide between the two health states. You may get to a point where at x days in Life B (for example, 4 days) they prefer Life B but an increase in 1 day (to 5 days) switches their preference so that they now prefer Life A. At this point you will expect the point where they cannot choose to lie somewhere between 4 and 5 days (the points at which their preferences changed). Ask the participant if they think the point at which they cannot choose between Life A or Life B is one of those numbers of days (4 or 5 in this example) or somewhere in between. Try not to suggest numbers to them but let them know they can half or part of a day should they wish.
Note down the number of days the participant is willing to give up in ‘Life B’, perfect health, to avoid 14 days in Life A on the practice sheet and on the practice sheet. (i.e. 14 minus the number of days at which the participant could not decide between the two health states).
Repeat this task for the remaining two practice states.
The practice sheet will allow you to assess if the participant understands the task and is providing logical responses. First of all, place the health state cards on the practice sheet in the order the participant ranked them. Then underneath each card write the number of days they were willing to be in Life B that corresponds with that card. These are the numbers you will have written down on the data collection sheet. You are looking for logical responses i.e. the number of days in Life B should increase (or at least not decrease) from the best to worst health states. If the responses don’t seem logical, remember there are no right or wrong answers but ask the participant if they thinks their responses make sense looking at them on the practice sheet. Ask them if they would change any of their responses while talking them through what their responses mean. Spend as much time as necessary until the participant understands the TTO process.
Symptom Specific Profiles
Following the practice session, we now move onto the main part of the TTO task, evaluating health states associated with the adverse-effect of the interventions in the trial. Explain to the participant that they do not have to have had any of these symptoms described in the health state profiles, they just need to imagine himself being in these health states.
Ask the participant to read the health state profiles and rank the health states from the best to the worst. Write down the order chosen by the participant. Let them know they can take their time at this point as it is essential they read through all the cards thoroughly.
Explain that the task will work in exactly the same way as the practice tasks: On the board, one health state or ‘Life A’ is going to last for 14 days—this will not change. The other health state or ‘Life B’ will vary in how long it lasts—up to a maximum of 14 days.
Shuffle the cards so that they are not in the order the participant ranked them. Let the participant know you are doing this and that the cards will be presented in a random order. Place the first profile card opposite the marker for ‘Life A’.
Place the ‘perfect health’ card opposite the marker for ‘Life B’.
Ask the participant to read these health states again out loud and to try to imagine themselves in these health states.
Move both markers to 14 days and ask the participant the following question: Would you prefer ‘Life B’, perfect health, for 14 days followed by a quick and painless death or would you prefer ‘Life A’ for 14 days followed by a quick and painless death?
Presumably, the participant will make the logical decision to choose Life B. Therefore, move the marker next to ‘Life B’ to 1 day and ask the participant the following question: Would you prefer 1 day in ‘Life B’ followed by a quick and painless death or would you prefer ‘Life A’ for 14 days followed by a quick and painless death? Or would you not be able to choose between the two?
Continue asking this question for the scenario where ‘Life B’ lasts for 13 days, 2 days, 12 days, 3 days, 11 days, 4 days, 10 days, 5 days, etc. until the participant cannot decide between the two health states. Follow the same procedure as in the practice for identifying the number of days in perfect health that are equivalent to 14 days in Life A.
Note down the number of days at which the participant is indifferent between the two health states on the data collection sheet.
Repeat this task for the remaining five profiles.
End the interview
At the end of the TTO process, ask the participant about how difficult they rate the interview task and any comments they have on the interview. Conclude the interview and thank the participant.
Chained TTO interview script (underline) and instructions
Introduction
Interviewer introduce oneself and thank the participant for their time. Indicate that it is expected to spend up to 1 hour on this interview. Ask the participant if they have any questions before the interview begins. Take written consent from the participant.
Ask the participant to fill in the consent form and the ‘TTO Study—Data Collection Form’. Let the participant know that the data collection form is just to provide details which will help with the analysis later on. All details will be kept anonymous and confidential.
Reiterate that the interview is voluntary and can finish at any time that they wish.
Format and Purpose of the interview
The interview we will be doing today is a little different to any interview you may have done before, but don’t worry we will explain everything fully as we go along and run through a practice at the beginning to make sure you are comfortable with the task. What we will be doing today is an activity called a time trade off exercise which is a tool used by health economists to put a number on how you value a particular state of health. We are going to use this board [point at the TTO board] throughout the interview and each of these cards is going to describe and represent a particular state of health. I will call these cards health states. We are going to ask you to imagine yourself in these health states and think about how you may feel in a situation where your heath is as it is described on the card. We are now going to do a practice run to help you understand how the interview works. There are no right or wrong answers in this practice session.
Practice Exercise
I am first going to show you three health states. These are just general health states and do not bear any reflection on your actual health at the moment. I would like you to imagine how you might feel and be affected if your health was as described on each card.
Ask the participant to read the ‘practice profiles’ out loud and ask them to rank the health states from the best to the worst state. Remind participant that this is not ‘most like their health’ but is simply the best to worst at face value of each card. Write down the order chosen by the participant (they are labelled on the back of the card A-C).
Describe the task: On the board there are two lives A and B. ‘Life A’ is going to last for 14 days—this won’t change during the interview. ‘Life B’ will vary in how long it lasts—up to a maximum of 14 days.
Place one of the practice cards opposite the marker for ‘Life A’. In Life A you should imagine that your health is as described in this health state. You will be in that health state for 14 days then at the end of the 14 days you will return to full health.
Place the anchor state card opposite the marker for ‘Life B’. In Life B your health will be as it is described in this anchor state card. The length of time you spend in this health state will vary throughout the interview but as in Life A you will always return to full health at the end of the time.
Ask the participant to read these health states again and to try to imagine themselves in these health states.
Move both markers to 14 days and ask the participant the following question: Would you prefer ‘Life B’, the anchor state, for 14 days followed by a full recovery or would you prefer ‘Life A’ for 14 days followed by a full recovery?
Presumably, the participant will make the logical decision to choose Life A. If they do, move the marker next to ‘Life B’ to 1 day and ask the participant the following question: Would you prefer 1 day in ‘Life B’ followed by a full recovery or would you prefer ‘Life A’ for 14 days followed by a full recovery? Or would you not be able to choose between the two?
Continue asking this question for the scenario where ‘Life B’ lasts for 13 days, 2 days, 12 days, 3 days, 11 days, 4 days, 10 days, 5 days, etc. until the participant cannot decide between the two health states. You may get to a point where at x days in Life B (for example, 4 days) they prefer Life B but an increase in 1 day (to 5 days) switches their preference so that they now prefer Life A. At this point you will expect the point where they cannot choose to lie somewhere between 4 and 5 days (the points at which their preferences changed). Ask the participant if they think the point at which they cannot choose between Life A or Life B is one of those numbers of days (4 or 5 in this example) or somewhere in between. Try not to suggest numbers to them but let them know they can half or part of a day should they wish.
Note down the number of days the participant is willing to be in ‘Life B’, the anchor state, to avoid 14 days in Life A on the practice sheet.
Repeat this task for the remaining two practice states.
The practice sheet will allow you to assess if the participants understand the task and are providing logical responses. First of all place the health state cards on the practice sheet in the order the participant ranked them. Then underneath each card write the number of days they were willing to be in Life B that corresponds with that card. These are the numbers you will have written down on the data collection sheet. You are looking for logical responses i.e. the number of days in Life B should increase (or at least not decrease) from the best to worst health states. If the responses do not seem logical, remember there are no right or wrong answers but ask the participant if they think their responses make sense looking at them on the practice sheet. Ask them if they would change any of their responses while talking them through what their responses mean. Spend as much time as necessary until the participant understands the TTO process.
Symptom Specific Profiles
Following the practice session, we now move onto the main part of the TTO task, evaluating health states associated with the adverse-effect of the interventions in the trial. Explain to the participant that they do not have to have had any of these symptoms described in the health state profiles, they just needs to imagine themselves in these health states with these particular symptoms.
Ask the participant to read the health state profiles and rank the health states from the best to the worst. Write down the order chosen by the participant. Let them know they can take their time at this point as it is essential they read through all the cards properly and thoroughly.
Explain that the task will work in exactly the same way as the practice tasks: On the board, one health state or ‘Life A’ is going to last for 14 days—this will not change. The other health state or ‘Life B’ will vary in how long it lasts—up to a maximum of 14 days.
Shuffle the cards so that they are not in the order the participant ranked them. Let the participant know you are doing this and that the cards will be presented in a random order. Place the first profile card opposite the marker for ‘Life A’.
Place the anchor state card opposite the marker for ‘Life B’.
Ask the participant to read these health states again out loud and to try to imagine themselves in these health states.
Move both markers to 14 days and ask the participant the following question: Would you prefer ‘Life B’, the anchor state, for 14 days followed by a full recovery or would you prefer ‘Life A’ for 14 days followed by a full recovery?
Presumably, the participant will make the logical decision to choose Life A. Therefore, move the marker next to ‘Life B’ to 1 day and ask the participant the following question: Would you prefer 1 day in ‘Life B’ followed by a full recovery or would you prefer ‘Life A’ for 14 days followed by a full recovery? Or would you not be able to choose between the two?
Continue asking this question for the scenario where ‘Life B’ lasts for 13 days, 2 days, 12 days, 3 days, 11 days, 4 days, 10 days, 5 days, etc. until the participant cannot decide between the two health states. Follow the same procedure as in the practice for identifying the number of days in the anchor state that are equivalent to 14 days in Life A.
Note down the number of days the participant is willing to be in ‘Life B’, the anchor state, to avoid 14 days in Life A on the data collection sheet.
Repeat this task for the remaining five profiles.
Valuing the Anchor State
The last task is to work out the participant’s preference for the anchor state. This requires another practice task as this is slightly different from the previous tasks.
As before, on the board, one health state or ‘Life A’ is going to last for 14 days—this will not change. However, at the end of the 14 days rather than recovering you will die a quick and painless death. The other health state or ‘Life B’ will vary in how long it lasts—up to a maximum of 14 days and again at the end of the time you will die a quick and painless death.
Place one of the practice profile cards opposite the marker for ‘Life A’.
Place the ‘perfect health’ card opposite the marker for ‘Life B’.
Ask the participant to read these health states again and to try to imagine themselves in these health states. Perfect health is anything the participant believes it to be.
Move both markers to 14 days and ask the participant the following question: Would you prefer ‘Life B’, perfect health, for 14 days followed by a quick and painless death or would you prefer ‘Life A’ for 14 days followed by a quick and painless death? This is an unusual question to ask so please let the participant know that it is understandable for it to be difficult to imagine but ask them to try.
Presumably, the participant will make the logical decision to choose Life B. Therefore, move the marker next to ‘Life B’ to 1 day and ask the participant the following question: Would you prefer 1 day in ‘Life B’ followed by a quick and painless death or would you prefer ‘Life A’ for 14 days followed by a quick and painless death? Or would you not be able to choose between the two?
Continue asking this question for the scenarios where ‘Life B’ lasts for 13 days, 2 days, 12 days, 3 days, 11 days, 4 days, 10 days, 5 days, etc. until the participant cannot decide between the two health states.
Note down at what day the participant is indifferent between the two health states on the practice sheet.
This is the end of the practice task, ask the participant if they understand the task, if they have any questions and if they are happy to move on.
To Value the Anchor State
Place the anchor state opposite the marker for ‘Life A’.
Place the ‘perfect health’ card opposite the marker for ‘Life B’.
Ask the participant to read these health states again and to try to imagine themselves in these health states.
Move both markers to 14 days and ask the participant the following question: Would you prefer ‘Life B’, perfect health, for 14 days followed by a quick and painless death or would you prefer ‘Life A’ for 14 days followed by a quick and painless death?
Presumably, the participant will make the logical decision to choose Life B. Therefore, move the marker next to ‘Life B’ to 1 day and ask the participant the following question: Would you prefer 1 day in ‘Life B’ followed by a quick and painless death or would you prefer ‘Life A’ for 14 days followed by a quick and painless death? Or would you not be able to choose between the two?
Continue asking this question for the scenarios where ‘Life B’ lasts for 13 days, 2 days, 12 days, 3 days, 11 days, 4 days, 10 days, 5 days, etc. until the participant cannot decide between the two health states.
Note down at what day the participant is indifferent between the two health states on the Collection sheet.
End the interview
At the end of the TTO process, ask the participant about how difficult they rate the interview task and any comments they have on the interview. Conclude the interview and thank the participant.
Appendix 4: Dealing with Common Problems when Conducting a TTO
Common issue one: Participants benchmark health states being valued against their current health
There was a tendency for participants to relate the health profiles being valued to their own health and this could result in participants ranking health profiles by how much they resemble their own situation.
Solution: When the interviewer observes participants displaying this tendency during the practice section, the interviewer should re-emphasise that this exercise requires the participant to consider each health state at face value hypothetically and not in relation to their own health.
Common Issue Two: Reaching Equivalency
It has been observed that it can sometimes be difficult for participants to reach a point of indifference. For example, a participant would have a clear preference for 6 days in Life B over 14 days in Life A, however, once the time in Life B is reduced by just one day to 5 days, they would switch to prefer 14 days in Life A over 5 days in Life B.
Solution: When participants appear to be unable to reach a point of indifference, the interviewer would first verbalise in lay language the preferences they showed on the decision board, for example, “at this current point [refereeing to the slider on the decision board], that is 6 days spent in Life B, you think that is better than 14 days in Life A?” and once the participant confirms it, the interviewer would then move the slider to a different point and repeat “at this current point [referring to the slider on the decision board], that is now 5 days spent in Life B, you think that is worse than 14 days in Life A?” The verbalisation of their choices would sometimes help the participants to find an equivalent point. If they still unable to find an indifference point, the interviewer would suggest them choosing fractions of days and asked if they felt that there is a value in between these durations (5 or 6 days), for example, 5 ¼, 5 ½ or 5 ¾ days if they wish.
Common issue three: Valuing the Anchor state
Due to the severity of the anchor state which is purposely designed to be intuitively worse than all the states being valued, participants may be unwilling to trade as they consider any time in the perfect health state is better than 14 days in the anchor state, which sometimes lead to them prefer 0 day in perfect health to 14 days in the anchor state. As we purposely design the anchor state to be not worse than being dead, this creates a difficult situation.
Solution: While we would tell participants that the choice of spending 0 days in the perfect health state is perfectly acceptable, we would also remind them that 0 days in perfect health equates to ‘instant death’ and ask the participant whether they consider ‘instant death’ equivalent to 14 days in the anchor state. This may help the participants re-evaluate their choice. We also suggested the possibility of choosing fractions of days.
Appendix 5: Practice Sheets Used in Conventional and Chained TTO Interviews
Conventional TTO interview practice sheet example
Chained TTO interview practice sheet example
Appendix 6: Decision Board Used in TTO Interviews