Commodity Price Uncertainty in Developing Countries
Commodity export price uncertainty is typically measured as the standard deviation of the terms of trade, but this approach encounters at least three objections. First, terms of trade indices are unsuitable as proxies for commodity price movements per se. Secondly, the shortness of terms of trade time series makes them inappropriate as a basis for constructing time varying uncertainty measures. Thirdly, simple standard deviation measures ignore the distinction between predictable and unpredictable elements in the price process, and therefore risk overstating uncertainty. The paper examines the features of commodity price uncertainty in developing countries using a new data set of unique quarterly aggregate commodity price indices for 113 developing countries over the period 1957Q1-1997Q4. A total of six different uncertainty measures are constructed, which confirm the importance of distinguishing between predictable and unpredictable components in the price process when measuring uncertainty. A a positive and highly significant relationship between commodity export concentration and commodity price uncertainty is found for all the measures. No obvious link is found between a countryâ€™s regional affiliation and its exposure to uncertainty. Similarly, there is no apparent relationship between a countryâ€™s experience of uncertainty and the type of commodities which dominates its exports. The exception is oil producers, which face greater uncertainty. The greater uncertainty faced by these countries can, however, be attributed almost exclusively to discrete and well publicised discrete oil shocks. A GARCH based measure of uncertainty indicates considerable time variation in uncertainty. Uncertainty is sometimes characterised by discrete spikes, while uncertainty in countries exhibits a secular increase in uncertainty over time. The majority of countries have seen uncertainty which exhibits considerable persistence. It is not clear what lies behind the time variation in uncertainty, which cannot be explained with reference to relatively time invarying export concentration.
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- Tim Bollerslev, 1986.
"Generalized autoregressive conditional heteroskedasticity,"
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EERI RP 1986/01, Economics and Econometrics Research Institute (EERI), Brussels.
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