Measuring multi-membership in economic integration and its trade-impact. A comparative study of ECOWAS and SADC

One of intriguing aspects of African Regional Trade Agreements (RTAs) is the extent of multi-membership, where many Africa countries are members of more than one RTA. Using a gravity model for 25 countries and the years 1980-2006 we measure the extent of multi-membership and compare its impact in two major African Regional blocs, ECOWAS and SADC. We find that the impact of multi-membership critically depends on the characteristics of the multi-membership of regional integration initiatives. We find a positive impact if an additional membership complements the integration process of the original regional integration initiative: overlapping memberships had a much stronger and significant positive effect on bilateral trade within ECOWAS compare to an insignificant impact within SADC.