Research ArticleSOCIAL SCIENCES

Quantifying the negative impact of brain drain on the integration of European science

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Science Advances  12 Apr 2017:
Vol. 3, no. 4, e1602232
DOI: 10.1126/sciadv.1602232
  • Fig. 1 Eastern-Western European divergence.

    Global trends in cross-border collaboration by international region: 1996–2014. Source: SCImago Journal and Country Rank based on Scopus (40). Notably, the curves for Western (W.) Europe and Eastern (E.) Europe are, before 2004, characterized by a roughly constant offset, thereby satisfying the prior equal slope condition of the DiD framework.

  • Fig. 2 Comparing synthetic (counterfactual) and real cross-border collaboration after the 2004 EU enlargement.

    (A) SCM results for the fraction ft of cross-border publications and (B) the total number χt of cross-border publications. The solid curves represent the real data, whereas the dashed curves represent the estimates, Embedded Image and Embedded Image, measuring the counterfactual scenario of no 2004 EU enlargement. Estimates are made using the SCM (26), implemented using a control group of 26 non-EU countries to best fit χt (ft) for t < 2004 and then to extrapolate Embedded Image(Embedded Image) for t ≥ 2004 (see the Supplementary Materials). Note that the χt that represent the incumbent pre-2004 EU countries are divided by 10 to facilitate visualizing all the curves on the same scale. δ and δ(%) represent the difference between the real and synthetic curves after 2004, providing estimates of the “2004 EU entry” effect on cross-border European integration. (C and D) Estimation of the significance level of the SCM results using the permutation test (25). (C) For the intensive variable ft, each curve represents the absolute difference Embedded Image; dash-dotted red and blue curves correspond to the entrant and incumbent EU curves in (A), respectively. Of the 24 curves, the (red) EU entrant curve has the largest positive net difference after 2004. (D) For the extensive variable χt, each curve represents the percent difference Embedded Image. The four countries that exceed the average EU entrant curve are peripheral countries bordering the EU. (C and D) The additional colored curves correspond to the SCM difference calculated for each of the non-European control countries. Only the control country curves that passed SCM goodness-of-fit criteria for t < t* based on the mean squared error between the synthetic and real curve are shown (that is, to eliminate control countries with synthetic estimates that are either unreasonably noisy or not estimable).

  • Fig. 3 High-skilled mobility before and after the 2004 enlargement.

    (Top) Mobility matrices (Mij) showing the total mobility (head counts) from country i to j, with black cells indicating 0 observations. The red color scale to the left of each Mij represents Embedded Image, with black cells indicating Δi < 4 for 1997–2004 and Δi < 155 for 2005–2012; the green color scale indicates log10Mij and is split into six equally spaced regimes in logarithmic scale. (Middle) Aggregate mobility by country: total outgoing Embedded Image, incoming Embedded Image, net mobility Embedded Image, and mobility polarization Embedded Image). (Bottom) MST representation of the mobility networks indicated by the orange links, with green links providing an overlay of the non-MST links. The thickness and opacity of links are nonlinearly related to log10Mij so that only the most prominent links are visible; color values are not comparable between the two time periods.

  • Fig. 4 High-skilled net mobility networks (Δij), before and after the 2004 EU enlargement.

    (Top) Mobility between the 2004/2007 entrant countries (“E”) and the rest of the incumbent European countries (“W”). The networks in each period are calculated from a total of 43,075 head counts (1997–2004) and 272,813 head counts (2005–2012), respectively. Link thickness represents the fraction of the total mobility. (Bottom) Node color represents EU entry year group (gEU,i); node size is proportional to the mobility polarization, 1 + Bi (with larger values indicating larger mobility out of country i); link thickness is proportional to log(|Δij|)2 between countries i and j, with the arrow pointing in the direction of the net flow and link color corresponding to the source node. The size/thickness scales used for both networks are the same, facilitating direct comparison.

  • Fig. 5 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 ≤ 0.001. (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.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/4/e1602232/DC1

    Supplementary Materials and Methods

    fig. S1. Supplementary SCM results.

    fig. S2. SCM: cross-border publication rate f.

    fig. S3. SCM: total cross-border publications χ.

    fig. S4. International collaboration rates and high-skilled labor mobility.

    fig. S5. Country-country mobility networks before and after the 2004 enlargement.

    fig. S6. Community structure of the high-skilled mobility networks.

    fig. S7. Consistency check for the significance of the EU entry effect.

    fig. S8. Comparison of high-skilled to total migration by country-country pair.

    fig. S9. Net flow of high-skilled labor: before and after the 2004 enlargement.

    fig. S10. Mobility success rates by country: before and after the 2004 enlargement.

    fig. S11. Mobility success rates by country-country pair: before and after the 2004 enlargement.

    fig. S12. Validation of the SCImago cross-border counting scheme.

    table S1. Full panel regression model results.

    References (4352)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Materials and Methods
    • fig. S1. Supplementary SCM results.
    • fig. S2. SCM: cross-border publication rate f.
    • fig. S3. SCM: total cross-border publications χ.
    • fig. S4. International collaboration rates and high-skilled labor mobility.
    • fig. S5. Country-country mobility networks before and after the 2004 enlargement.
    • fig. S6. Community structure of the high-skilled mobility networks.
    • fig. S7. Consistency check for the significance of the EU entry effect.
    • fig. S8. Comparison of high-skilled to total migration by country-country pair.
    • fig. S9. Net flow of high-skilled labor: before and after the 2004 enlargement.
    • fig. S10. Mobility success rates by country: before and after the 2004 enlargement.
    • fig. S11. Mobility success rates by country-country pair: before and after the 2004 enlargement.
    • fig. S12. Validation of the SCImago cross-border counting scheme.
    • table S1. Full panel regression model results.
    • References (43–52)

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