A recent report from "State of the Developer Nation Q1 2017" provides an interesting insight with this key finding:
"We’re still a long way off a global market for developers. The median earnings of web developers in Western Europe are half of those of their North American counterparts; web developers in other regions earn half again. This opens up arbitrage opportunities for developers willing to work remotely".
"The best developers in those regions (Asia, the Middle East, Africa) work for multinationals or sell their services on international marketplaces"
View the report here: direct download link