The fact that studies on regional trade flows are relatively abundant can be explained by trade data being relatively well available, and of sufficient detail and good quality.
This is much less the case for data on capital flows, migration and flows of information. In the case of intra-regional migratory flows and stocks of immigrants,
for example, although it is essential information, in many countries the quality of the data is insufficient or the data are lacking. trade28 can easily be calculated. A proposal for a combined set of indicators on (trade) regionalisation has been made by Bensidoun and Chevallier (1998) (table 7)