It seems unlikely to me that a re-evaluation of how many QALYs buying a sandwich is worth would arise from a re-evaluation of how valuable QALYs are, rather than a re-evaluation of how much buying the sandwich is worth.
I disagree with this. The value of a QALY could depend on other features of the universe (such as your lifespan) in ways that are difficult to explicitly characterize, and thus are subject to revision upon further thought. That is, you might not be able to say exactly how valuable the difference between living 50 years and living 51 years is, denominated in units of the difference between living 1000 years and living 1001 years. Your estimate of this ratio might be subject to revision once you think about it for longer. So the value of a QALY isn’t stable under re-evaluation, even when expressed in units of QALYs under different circumstances. In general, I’m skeptical that the concept of good reference points whose values are stable in the way you want is a coherent one.
Maybe there is no absolutely stable unit, but it seems that there are units that are more or less stable than others. I would expect a reference unit to be more stable than the unit “the difference in utility between two options in a choice that I just encountered”.
I disagree with this. The value of a QALY could depend on other features of the universe (such as your lifespan) in ways that are difficult to explicitly characterize, and thus are subject to revision upon further thought. That is, you might not be able to say exactly how valuable the difference between living 50 years and living 51 years is, denominated in units of the difference between living 1000 years and living 1001 years. Your estimate of this ratio might be subject to revision once you think about it for longer. So the value of a QALY isn’t stable under re-evaluation, even when expressed in units of QALYs under different circumstances. In general, I’m skeptical that the concept of good reference points whose values are stable in the way you want is a coherent one.
Maybe there is no absolutely stable unit, but it seems that there are units that are more or less stable than others. I would expect a reference unit to be more stable than the unit “the difference in utility between two options in a choice that I just encountered”.