are no longer valid) would influence the contemporaneous migration flows beyond the impact exerted by the diaspora itself. For instance, it turns out that guest worker agreements did not create any preferential treatment at the level of country pairs in the migration policy. Therefore, it is expected that these guest worker agreements are not themselves correlated with the bilateral unobservable components. Examples of such a process are illustrated for instance by the impact of the post-war guest worker agreements between Belgium and Italy or Spain.

The second instrument proposed by Beine et al. (2010) is a variable capturing the unobserved diaspora in the 1960’s through a combination of variables representing some push factor in country i , size in country i, openness and size in country j and distance between i and j. We use four different measures. The basic measure is ln(popi ∗ immstj/distij)∗armedconflicti where popi is the population size in the 60’s of country i, immstj is the immigrant stock of country j in the 60’s, distij is the distance between i and j and armedconflicti is a dummy variable capturing the occurrence of armed conflicts in country i during the 60’s. To capture push-factors leading to emigration in the 1950s and 1960s, we only consider conflicts observed between 1946 and 1960. We distinguish minor conflicts (number of battle-related deaths between 25 and 999) denoted CONFL1 and wars (at least 1,000 battle-related deaths in a given year) denoted CONFL2. The variables CONFL1 and CONFL2 sum up the number of annual conflicts over the period 1946-1960. IV estimation methods are suited to address the issues (size, selection and concentration) listed above. Nevertheless, like OLS, they are subject to issues related to the selection bias. A combination of Poisson regression models along with IV estimation is proposed by Tenreyro (2009) within the GMM framework. This is relevant only for the size issues but it is nevertheless beyond the scope of this paper.

# 5 Results

After listing all the potential problems with the data, estimation methods and identification issues, we finally turn to the estimation of the three main equations listed above (2, 3 and 5) which correspond to analysis of the impact of diasporas on the size, skill composition and concentration of migration flows, respectively.

Table 1 reports the results for five different estimation techniques for the estimation of the impact of diaspora on migration flows. The techniques used are OLS (using lows as the dependent variable), Heckman two stage method with and without an instrument for the selection, Maximum likelihood Poisson and IV regression (on the flows as well) using the two above mentioned instruments. The results illustrate the strong robustness of the estimation of the key elasticity parameter which ranges between 0.62 and 0.76. This means that a 1% increase in the size of the migrant network present in the destination country in 1990 tends to increase the subsequent migrant flow from a given origin country over the next ten years by around 0.7%. This result is in line with some of the previous results in the literature using the US data. For instance, focusing only 13