affected negatively and significantly by road distance. In all cases, the effect of road quality is low. For rice in column (6) of table 3, once controlling for the distance separating towns, increasing the share of road paved between two cities by 10 percentage point would have the same effect as an increase of distance of 1 additional kilometer (=exp(0.10*0.0527/0.06)).

Second, in columns (3), the coefficient on the single dummy for the existence of a border between towns is positive and highly significant. This means that impediments to trade in the region are on average higher between countries than within countries. After controlling for intertown distance and road quality, price differentials for towns separated by a border are 7.7% (=exp(0.0742)-1) higher. This suggests that dealing with policy barriers at the border can be as important as infrastructure spending that increases the quality of roads in delivering greater market integration for food products. Our estimated coefficients on the border dummy are slightly higher in terms of magnitude than those obtained by Aker et al (2012) for Cowpea and Millet between Niger and Nigeria (of around 2%).

Comparing with the literature, the effects in terms of price differences are slightly higher than those found by Broda and Weinstein for Canada and US (of around 7%) and a bit lower than Versailles (2012) for staple food between Uganda, Burundi, Tanzania and Kenya (of around 9%). However our estimated distance coefficient is much higher than the distance coefficient reported by Broda and Weinstein (2008) for Canada and US reflecting unsurprisingly that distance plays a much bigger role in Eastern and Central Africa. The effect of distance is also slightly higher than in Versailles (2012), who finds a distance coefficient of around 0.015 for staple foods (i.e. for rice, maize potatoes and sweet potatoes). Computing a distance-equivalent as suggested by Engel and Rogers (1996), we find that crossing a border in the region impedes market integration by the same amplitude as increasing the distance between cities by 8km (computed as exp(0.0742/0.0352)) while Versailles finds a distance equivalent of 220km and Broda and Weinstein of around 328km. The low distance equivalent reveals the predominance of the effect of distance on market integration in the region. Araujo and Brunelin (2013) found similarly a small border effect in West Africa between Benin, Burkina Faso, Mali and Niger for mil, sorghum and maize, between 2km and 35km.<sup>16</sup> Many factors could explain that the border effects between African countries are relatively low. First, the high number of weighbridges and policy controls along intra-national roads increase transport delays and, therefore, constitute substantial barriers to trade within African countries. Second, within-country differences of ethnicity and language could explain the low domestic market integration. Third, the lack of control at the border and the corruption of customs may facilitate trade of primary commodities between countries; which is reflected in the large amount of informal trade estimated by Stryker (2012) based on FEWSNET data. For example, according to Stryker (2012), 15’815 MT of Maize have been informally traded between Tanzania and Kenya in 2011. In this regard, it is less surprising that the estimated average border coefficients between African countries are low compared with the effect of distance.

> 16 As these authors argue, the distance equivalent proposed by Engel and Rogers (1996) is unitless, i.e. it does not vary according to the measurement unit for distance. However, it is usual to express it in terms of the unit of measurement of distance in the sample, which is in kilometers in this paper.

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