They can originate from the demand side such as economic expansions or recessions, or from the supply side through reduced supply of inputs, availability of substitutable/complementary products or, typically, energy markets. Finally, shocks can be transmitted through macroeconomic variables such as exchange rates and terms of trade. Balcombe (2008) finds that the volatility of most individual food commodities is positively related to the general volatility of other agricultural commodities.