One of the flaws of "national" debt, is that it is really only a measure of government debt. But 80% of our economy is in the private sector (other than federal, defense, and state & local governments). To arrive at the real "national" debt, you need to take into account not only the government debt (relatively small) but also private credit market debt. So discuss this chart:
It provides quite a different (and more disturbing) picture than jfern's chart.
I just love how it spikes in the years 1980-1988. Gee whiz, wonder why.
