South-North trade in Ireland: Gravity and firms from the Good Friday Agreement to Brexit

This paper revisits the work of Fitzsimons et al. (1999) on the level of trade between Ireland and Northern Ireland. In doing so, we reflect on the recent move to prominence of this issue since the referendum decision of the UK to leave the EU and also on the shift within the economics literature to looking at trade issues from a micro rather than a macro perspective as data availability has grown. Our country-level results show the same pattern of limited statistical significance for a border effect as was found in the earlier work still holds, but when using firm-level data we find a positive and significant border effect. This effect holds for total trade at firm and product level with the primary determinant coming from the intensive margin, both in terms of average exports per firm and average exports per product within firms.