The sort of basic observations that R&D spending has increased but economic growth has remained roughly the same seems to imply the obvious conclusion that productivity is declining.
That does seem like the most likely conclusion, but another obvious interpretation of “X doesn’t change when we increase Y” would be “maybe Y doesn’t actually affect X in the first place”. For instance, maybe funding above some threshold is all eaten by parasites, or maybe the bottleneck on growth speed is something other than formal R&D (e.g. good ideas might strike randomly regardless of whether you’re a researcher or not, and the official “researchers” just “harvest” the insights that are already “in the air” thanks to the general population).
(Most of my probability mass is still on “productivity is declining.”)
That does seem like the most likely conclusion, but another obvious interpretation of “X doesn’t change when we increase Y” would be “maybe Y doesn’t actually affect X in the first place”. For instance, maybe funding above some threshold is all eaten by parasites, or maybe the bottleneck on growth speed is something other than formal R&D (e.g. good ideas might strike randomly regardless of whether you’re a researcher or not, and the official “researchers” just “harvest” the insights that are already “in the air” thanks to the general population).
(Most of my probability mass is still on “productivity is declining.”)