You are correct that it is not. Galbraith has made the point elsewhere that it isn't.
"Galbraith's response what that flat out there is no evidence to support it. What? What about Rogoff/Reinhart's "This time it's different"? That book and its research reiterates the debt/GDP ratio rule of thumb that is taken very seriously, and has filtered out to the mainstream very effectively via Peterson, etc...
Why didn't Galbraith acknowledge that research? Is it rogue research or obviously flawed? "
It is obviously flawed a colleague of Galbraith does a take down here:
http://www.rooseveltinstitute.org/new-roosevelt/going-rogoff
The short form is this, although they have a large data set their presentation of it is comical. the idea that 18th century public finance for countries under the gold standard is in any way comparable to public finance in a world without a gold standard is absurd. They also mix up private debt, public debt and countries with large amounts of foreign currency denominated debt. that is obviously very different from the u.s which only had debt in the unit of account of the u.s dollar. Finally, they also mix up causality. a big recession (especially one caused by bubble driven financial crisis) causes tax revenues to fall and payouts on things like unemployment insurance to rise. this will lead to high debt to GDP ratios. however, it didn't cause the big recession. It's the equivalent to the old joke about umbrellas causing rain.
a last note: mixing up high public debt and high private debt is absurd because the financial liabilities of the public sector are assets to the private sector. The large Clinton surpluses were the major driving force behind the run up in private debt relative to GDP in the late 1990's. The only reason it didn't cause a big recession then was because of the housing bubble.
-- -Nathan Tankus -----------------------------------------------------------------------------------------------------------------------------------------------