You could have seven groups with varying levels of choice: group 1 is forced to be vegan, group 4 is the control group, and group 7 is forced to consume meat. Groups 2-3 would be nudged vegan, 5-6 would be nudged to eat meat.
Measure them all and get happiness and health curves after 5, 10, 15 years.
It would be expensive, but probably a better use of money than a lot of other stuff.
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You could have seven groups with varying levels of choice: group 1 is forced to be vegan, group 4 is the control group, and group 7 is forced to consume meat. Groups 2-3 would be nudged vegan, 5-6 would be nudged to eat meat.
Measure them all and get happiness and health curves after 5, 10, 15 years.
It would be expensive, but probably a better use of money than a lot of other stuff.