Figure 2. Distribution of the BTA impact indices Πin (purple) and Πout (blue) for the 107 BAAs implemented between 1995 and 2008 (dark colours, see Table 1 in the Annex for a complete list). The bright colors show the corresponding results for the 15,199 pairs of countries that have not negotiated bilateral agreements, assuming an arbitrary reference year 2002. Each of the four distributions is normalized to one and thus maps the relative frequency. Note the logarithmic scaling of the empirical frequencies displayed. Switzerland (which has a customs union with Liechtenstein, which is sometimes included in the agreements) has bilateral agreements with the following countries and blocs: Given this compromise, we have set αmax in all the calculations in section 3 at twice the average length of the journey between the two itn subgraphs C1 and C2. It should be noted that this simple analysis does not establish a causal link directly with the implementation of the FTA, resulting in more closely intertwined economic relations, as it would also be consistent with the statement that countries with generally more positive economic development have a greater tendency to negotiate trade agreements. Further studies on this aspect would be needed to deepen this point. In general, it is clear from the estimated probability distributions that positive BTA indices are more common than negative values. .