The Effects on Growth of Commodity Price Uncertainty and Shocks
The author estimates the effects on growth of commodity price shocks, and uncertainty within an established empirical growth model. Ex-post shocks, and ex-ante uncertainty have been treated in the empirical literature as if they were synonymous. But they are distinct concepts, and it is both theoretically, and empirically inappropriate to treat them as synonymous. He shows that the interaction between policy, and aid is robust to the inclusion of variables capturing commodity price movements. More important, his approach departs in three ways from earlier empirical studies of the subject: 1) It deals with issues of endogeneity, without incurring an excessive loss of efficiency. 2) It defines the dependent variable to allow an assessment of the longer-term implications of temporary trade shocks. 3) It imposes no priors on how commodity price movements affect growth, but compares and contrasts a range of competing shock, and uncertainty specifications. The author resolves the disagreement about the long-run effect of positive shocks on growth, finding that positive shocks have no long-run impact on growth (that windfalls from trade shocks do not translate into sustainable increases in income). He shows that negative shocks have large, highly significant, and negative effects on growth, but that commodity price uncertainty does not affect growth.