1. Fig. 5 The impact of EU enlargement and mobility on cross-border collaboration.
The impact of EU enlargement and mobility on cross-border collaboration. (A) Point estimates with 95% confidence intervals. Two variables are particularly important to our analysis: (i) βT captures the interaction between dummy values for before/after 2004 and a country’s EU membership status—that is, the impact of EU entry; (ii) βB captures the variation due to mobility polarization, Bi,t. We ran two regression models, each with a different baseline set of countries to demonstrate the robustness of our results. In the first model (magenta data, “full model”), the incumbent EU members serve as the baseline because their EU membership status does not change over the period of the analysis (Nobs. = 4494, adjusted R2 = 0.66, and Nc = 31 countries). In the second model (orange data, three-period model), we used the 2007 entrants (BG and RO) as the baseline comparison for the 2004 entrants over three periods from 2001 to 2006 (Nobs. = 504, adjusted R2 = 0.60, and Nc = 12 countries). See eq. S4 for the model specification and table S1 for the full set of controls, as well as other partial models demonstrating robustness of our results. Parameters are estimated using country fixed effects and robust SEs implemented by the Huber/White/sandwich estimator, which accounts for cross-sectional heteroscedasticity and within-panel (serial) correlation. As a visual aid, asterisks indicate the level of significance for each coefficient estimate: *P ≤ 0.05, **P ≤ 0.01, ***P ≤ (B) The marginal effect of Bi,t on fi,t, calculated using an interaction term between EU membership status and Bi,t. The main results of this model are two partial coefficients: βB|E.Eur. for the entrants and βB|W.Eur. for the other Western countries. Holding all other covariates at their mean value, comparison of the marginal linear predictions indicates that a country in the Western European group with B = 1 still has a higher expected level of international collaboration than a country from the Eastern European group with B = − 1. Shaded interval indicates the 95% confidence interval calculated using the δ method.
Omar A. Doria Arrieta et al. Sci Adv 2017;3:e
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