In Europe, the correlation between economic strength and the strength of the shadow economy is pretty strong.  Every country studied on the continent - excluding Albania, Bulgaria, and Ukraine - has a shadow economy that takes up at most one-third of its overall economy.

In South America, the correlation between economic strength and the strength of the shadow economy is pretty weak.  Every country studied on the continent, excluding Chile, has a shadow economy that takes up at least one-fifth of its overall economy.

In North America, the indirect correlation between economic strength and the strength of the shadow economy is very strong.  The United States and Canada have by far the largest economies and the smallest proportion of underground activity.