I thought some folks here would appreciate the perspective provided by the table below.
The data are almost a year old now, but likely relatively accurate.
This was somewhat of a surprise to me considering the content and tone of business "news" I read daily.
One could argue that in some countries, like China, a significant amount of GDP has yet to be monetized via its public markets and thus is not reflected in the table.
Link:
http://finance.mapsofworld.com/financial-market/world-share/