Interesting. Previous analyses I’ve seen show a sloping off of happiness vs. income, but I’m not sure if they used PPP (purchasing power parity) as opposed to per capita GDP. (Roughly speaking, PPP adjusts GDP for differences in costs of living different countries.)
Some (achem, Pielke, achem) have thought of this saturating function as being “disproven” because a recent paper saw that the relation was linear — if you used a log scale for income! Suffice it to say, I’m willing to believe that happiness continues increasing at higher incomes but requires exponential increases at higher incomes, but (a) that still mitigates against allocating resources to the most well-off as you’re definitionally getting less “bang for your buck”, and (b) all biological systems have a saturation point, so (some) economists’ unhinged fantasies aside, a saturating function *must* represent happiness’s relationship to income.
This piece implies the relationship might flip at some point, which I would also find plausible.