The original theory underlying the Rahn Curve assumed that as the size of government increased from zero, supplying law and order and some basic services, economic growth rates would increase until government reached some optimal size.

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But it is a nice object lesson in the basic economic proposition first put forward by David Ricardo as the Iron Law of One Price.

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The poorest countries can hope to catch up if they establish the basic economic institutions (starting with property rights and the rule of law) and do lots of other things right.

ECONOMIST: A century of progress