Export product concentration declined over time for all country groups in Sub-Saharan Africa —although at different paces across the different groups. Countries that were abundant in minerals and metals experienced the largest decline in the Herfindahl index of product concentration: it dropped from 0.69 in 1990-94 to 0.46 in 2010-14. In the case of oil rich countries, the pace of decline was slightly slower than that of metal exporters, but the group maintained the largest degree of export product concentration by 2010-14 (0.67). Finally, non-resource rich countries exhibit the lowest degree of export product concentration in 2010-14 (0.21, down from 0.29 in 1990-94).

The evolution of export market concentration differs sharply across groups in Sub-Saharan Africa. The Herfindahl index of market concentration among non-resource rich countries remained almost invariant over time — as is also the case for the region as a whole. Export market concentration for oil rich countries declined sharply from 0.30 in 1990-94 to 0.15 in 2010-14 while that of countries abundant in minerals and metals increased from 0.08 in 199094 to 0.28 in 2010-14. Overall, oil rich countries tend to have a more diverse group of trading partners than minerals and metals-rich countries in 2010-14.

# 3.3 Natural Resources in Exports

There is no consensus in the literature about the effect of natural resources on growth —see for instance Havranek et al. (2016) for a meta-analysis of the long-term growth effects of natural resource richness. Before digging deeper and trying to understand the growth effects of natural resources, we explore the evolution of different indicators of trade in natural resources across regional country groups. The set of indicators of natural resource intensity in economic activity include natural resource exports as a share of GDP and natural resource exports as a share of total exports. For this information, we used the World Integrated Trade Solution (WITS) database on the SITC, Revision 1.0. Natural resource exports comprise the commodities in the SITC sections 0 – food and live animals, 1 – Beverages and tobacco, 2- Crude materials, inedible except fuels (excluding 22 – oil seeds, oil nuts and oil kernels), 3 – mineral fuels, lubricants and related materials, 4 – animal and vegetable oils and fats, and 68 no ferrous metals (Lederman and Maloney 2007). The value of these exports (in US dollars at current prices) is then normalized by either GDP or total merchandise exports.

## **3.3.1 Natural resource exports as a share of GDP**

Natural resource exports as a percentage of GDP in the Sub-Saharan Africa region declined from 17 percent in 1990-94 to 13.2 percent in 2010-14. The decline in this ratio for oil rich countries is comparable to that of the region, although the share of natural resources in GDP is the largest across all country groups (about 43 percent in 2010-14). The share of natural resource exports in GDP for countries rich in minerals and metals had the largest decline (from 27 percent in 1990-94 to 16 percent in 2010-14). Finally, natural resource exports of non-resource rich countries remained stable over time at about 9 percent of GDP.

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