[smithbits]

And here's the IMF study it's based on http://www.imf.org/external/pubs/ft/fandd/2011/09/Berg.htm

[john_b]

That one is fairly short and is mostly an overview of prior work. I think the original sources he's referencing are these: http://www.imf.org/external/pubs/ft/sdn/2011/sdn1108.pdf http://www.imf.org/external/pubs/cat/longres.cfm?sk=21769.0