The [quality-adjusted] life-year as a unit has not changed. Not ever.
I believe this is wrong. It is my understanding that the quality-adjusting of life-years is a type of utility adjustment. The disutility (inconvenience, cost, life dissatisfaction) of a health condition can certainly change over time.
Consider, for example, a low-extremity disability such that you cannot walk. If you, or someone like you, experienced such a disability 100 years ago, your change in quality of life would likely be different than if you experienced it today. Your relative disutility from that disability would probably be lower today than a century ago and, in part, for reasons having nothing to do with health care. I’ll give you two examples.
First, the nature of the job market is different today than a century ago. There are many more jobs that don’t require use of one’s lower extremities today. I work in one. It’s the ubiquitous office job. All I really need to do my job is my brain, the vital organs that make it work, and a computer with an internet connection. Eyes help a lot, as do use of hands and arms. As much as I like them, my legs hardly matter for my work. Such jobs were not as common many decades ago. So, for access to work alone, were I a person with a lower extremity disability I’d be better off today.
Second — and here I am speculating a bit — the difference in cost (including time cost) of a mile of transportation is not so different today between persons with and without a lower extremity disability. Assistive devices, public transportation (in some areas) and readily available motor vehicle modifications make it so. That’s not to say those don’t cost something.
A century ago, I imagine the cost of a mile of transportation was much higher for someone who could not walk than for someone who could. A lot more transportation was by foot or by means that require use of lower extremities (horse, say). The relative disutility of life without use of legs for this reason was probably higher than it would be today.
For these, and other reasons, the quality-adjusted life-year (QALY) of a lower extremity disability may be higher today than a century ago. Consequently, it is not true that QALYs don’t change over time.
For all that, I am still not convinced that we can or should ignore quality-adjustment when considering productivity changes in the health sector. Baumol didn’t convince me. Can you?