Total US debt to GDP was stable at around 150% until 1980 when it began to rise, topping out at 400% in 2009 and settling around 360% since then. This debt incr

Total US debt to GDP was stable at around 150% until 1980 when it began to rise, topping out at 400% in 2009 and settling around 360% since then. This debt increase partially masked both slowing GDP growth due to demographics at the national level, and slowing productivity growth at the individual level. Regardless of the internal cause of slowing productivity growth, it did slow and maintaining the same debt to GDP ratio as before 1980 would have required accepting a standard of living that rose more slowly than it did. (GDP growth slowdown due to demographics washes out on a per capita basis.) It seems the most likely cause for the 1970s productivity slowdown was the oil shocks and the most likely cause for the 2000s productivity slowdown is the falling marginal return on research expenditures.