When it is said that the average American has x thousand dollars in debt....does the x thousand consist of everything: mortgage, student loan, line of credit, credit card overdue payments etc.? Or are some categories excluded from the calculation?
It really depends on the cited source and intention of the article it appears in. There are many ways of slicing data. Average total debt, average credit card debt, average card debt for those who carry balance, average mortgage debt, etc. Whatever you read may cite any of these numbers, there are many sources for this information, so really any statement of "total debt" with no supporting details is pretty meaningless.
Liz Weston has been on a crusade to set the record straight about how much debt people carry, but I don't think that this answers your question.
Like MrChrister commented, it really does depend on the sources cited by the author, and how careful they are when they define "total debt."
After all, if you make up a statistic, 73% people with total debt over $11,500 will actually believe you. ;)
I'm guessing that the statistics are based on the information from the credit reporting agencies, so it's most likely based on the debt reported to them, which would be mortgages, loans (official loans, like from banks, not from friends and mobsters), credit cards, and liens and collections.
Debts not reported anywhere (for example, my friend owes me $5K that I helped him with for a new car) are probably not included in this statistics.