an MFA quota in the US (prior to 2005) and a weighted average of the presence of MFA quotas on competitor countries exporting that product to the US. The effect of the average MFA quota imposed on the rest of the world is insignificant.<sup>39</sup> Importantly, accounting for competition from other countries with preferential access to the US reduces only slightly the magnitude of the impact of AGOA on apparel products though the impact on GSP LDC products becomes insignificant.<sup>40</sup> Our evidence so far shows that the estimated impact of AGOA on apparel increases over time after its enactment 2001 but flattens after 2005. We conjecture that the MFA end in 2005 unleashed the exports of apparel from China and other Asian countries which mitigated substantially the positive impact of AGOA on apparel exports for African countries. The interesting question is whether this lack of durability in the AGOA apparel impacts is heterogenous across countries, as was hinted at in Section 4 by the differential raw data patterns across four groups of countries. We re-estimate Eq. (1) allowing the coefficient on the AGOA apparel term to vary across years and sub-regions: Central and West Africa, East Africa, and Southern Africa. We plot the corresponding coefficient estimates and 95 percent confidence intervals in Figure 3.

There is a clear difference across sub-regions in the temporal response to AGOA and to the end of the MFA.<sup>41</sup> For Central and West Africa, the impacts of AGOA on apparel exports to the US are mostly insignificant, and there are even signs of a negative impact in the early years.

> 39 Surprisingly, the effect of the own country-product quota dummy is positive and significant. This may reflect the fact that the MFA quota is endogenous to the export flows, i.e. it was more likely to be imposed when a country-product had experienced significant export growth to the US.

> 40 Online Appendix D presents the results from a robustness check, where we estimate the impact of tariff preferences granted by the US under different schemes using the data on US tariffs at country-product level for the period 1997-2017 instead of treatment indicators. The results indicate that on average US tariff preferences do not significantly increase export growth at the countryproduct level. However, when the effect is allowed to differ for African and non-African countries, US tariff preferences significantly increase export growth for African countries. When the effect is further allowed to differ across product groups, the results show that US tariff preferences have a significant positive impact on apparel export growth as well as manufacturing export growth from African countries. We view these results as consistent with those based on our triple-differences specification. 41 We also re-estimate Eq. (1) allowing the AGOA apparel term to have a different coefficient for each African country. Online Appendix D shows cross-country heterogeneity in the impact of AGOA on apparel. The countries with the largest significant positive impacts of AGOA on apparel exports to the US are Kenya, Madagascar, Eswatini, Ethiopia, and Lesotho. In contrast, South Africa, Senegal, Nigeria, and Côte d’Ivoire exhibit a negative impact of AGOA on their apparel exports to the US.

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