If you add up countries' reported trade balances, you don't get zero. Is the explanation Errors & Omissions? Or does Earth run a trade deficit with other planets? [As cited by Krugman's "Theory of Interstellar Trade."]
This paper claimed to refute the view that Ghana's cocoa farmers could be paid a below-market price by the national marketing board, without adversely affecting their output. After a review of the history, the elasticity of supply is estimated econometrically. Local rainfall is an exogenous variable and the lag structure is taken from biological growth pattern of the trees.