metadata: authors: 0: author: Beine, Michel
1: author: Docquier, Frederic
2: author: Ozden, Caglar
count: World
docna: 0: docna: Diasporas
docty: Policy Research Working Paper
theme: Other trade and integration
majtheme: Trade and integration
subtopic: Indigenous Peoples,Indigenous Peoples Law,Human Migrations & Resettlements,Educational Sciences,Social Cohesion,International Migration,Indigenous Communities,Migration and Development
teratopic: Culture and Development,International Economics and Trade,Health, Nutrition and Population,Social Development,Communities and Human Settlements
abstracts: cdata!: Migration flows are shaped by a complex
            combination of self-selection and out-selection mechanisms.
            In this paper, the authors analyze how existing diasporas
            (the stock of people born in a country and living in another
            one) affect the size and human-capital structure of current
            migration flows. The analysis exploits a bilateral data set
            on international migration by educational attainment from
            195 countries to 30 developed countries in 1990 and 2000.
            Based on simple micro-foundations and controlling for
            various determinants of migration, the analysis finds that
            diasporas increase migration flows, lower the average
            educational level and lead to higher concentration of
            low-skill migrants. Interestingly, diasporas explain the
            majority of the variability of migration flows and
            selection. This suggests that, without changing the
            generosity of family reunion programs, education-based
            selection rules are likely to have a moderate impact. The
            results are highly robust to the econometric techniques,
            accounting for the large proportion of zeros and endogeneity problems.
repnme: repnme: Diasporas
display_title: Diasporas
listing_relative_url: /research/2009/07/10766792/diasporas
topicv3: In-Migration m1326035 2204,Education, Skills Development and Labor
            Market m1326135 1484,Indigenous Peoples m1326947 749,Education m1327048 470,Immigration m1504162 2837
publishtoextweb_dt: 2010-07-01T00:00:00Z
historic_topic: Culture and Development,International Economics and Trade,Health, Nutrition and Population,Social Development,Communities and Human Settlements
no_of_pages: 41
model_extractions: WPS4984 Policy Research Working Paper 4984

# Diasporas

_Michel Beine Frédéric Docquier Çağlar Özden_ The World Bank Development Research Group Trade and Integration Team July 2009
Policy Research Working Paper 4984

# **Abstract**

Migration flows are shaped by a complex combination of self-selection and out-selection mechanisms. In this paper, the authors analyze how existing diasporas (the stock of people born in a country and living in another one) affect the size and human-capital structure of current migration flows. The analysis exploits a bilateral data set on international migration by educational attainment from 195 countries to 30 developed countries in 1990 and 2000. Based on simple microfoundations and controlling for various determinants of migration, the analysis finds that diasporas increase migration flows, lower the average educational level and lead to higher concentration of low-skill migrants. Interestingly, diasporas explain the majority of the variability of migration flows and selection. This suggests that, without changing the generosity of family reunion programs, education-based selection rules are likely to have a moderate impact. The results are highly robust to the econometric techniques, accounting for the large proportion of zeros and endogeneity problems.

This paper—a product of the Trade Team, Development Research Group—is part of a larger effort in the department to understand the impact of international migration on poverty and development. Policy Research Working Papers are also posted on the Web at http://econ.worldbank.org. The author may be contacted at cozden@worldbank.org.

_The Policy Research Working Paper Series disseminates the findings of work in progress to encourage the exchange of ideas about development issues. An objective of the series is to get the findings out quickly, even if the presentations are less than fully polished. The papers carry the names of the authors and should be cited accordingly. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the International Bank for Reconstruction and Development/World Bank and its affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent._ Produced by the Research Support Team
# Diasporas<sup>�</sup>

## Michel Beine<sup>a</sup> , Frédéric Docquier<sup>b</sup> and Ça1⁄4glar Özden<sup>c</sup>

> a University of Luxembourg and CES-Ifo

b FNRS and IRES, Université Catholique de Louvain, IZA-Bonn and CReAM-London. c World Bank, Development Research Group Abstract Migration ‡ows are shaped by a complex combination of self-selection and out-selection mechanisms. In this paper, the authors analyze how existing diasporas (the stock of people born in a country and living in another one) a¤ect the size and human-capital structure of current migration ‡ows. The analysis exploits a bilateral data set on international migration by educational attainment from 195 countries to 30 developed countries in 1990 and 2000. Based on simple micro-foundations and controlling for various determinants of migration, the analysis ...nds that diasporas increase migration ‡ows, lower the average educational level and lead to higher concentration of low-skill migrants. Interestingly, diasporas explain the majority of the variability of migration ‡ows and selection. This suggests that, without changing the generosity of family reunion programs, education-based selection rules are likely to have a moderate impact. The results are highly robust to the econometric techniques, accounting for the large proportion of zeros and endogeneity problems. JEL Classi...cation: F22, O15 Keywords: Migration, self-selection, network/diaspora externalities.

> �Earlier versions of this paper have been presented at the "Migration and Development" conference (Lille, June 2008), at the "Globablization and Brain Drain" conference (Tel Avid and Jerusalem, December 2008). The paper bene...tted from comments and suggestions by Luisito Bertinelli, Serge Coulombe, Caroline Freund, Eric Gould, Gordon Hanson, Will Martin, David McKenzie, Mario Piacentini, Samaschwar Rao, Hillel Rapoport, Assaf Razin, Mark Rosenzweig, Maurice Schi¤ and Antonio Spilimbergo. We would like to thank Sara Salomone for gathering data on guest workers’ agreements. The second author acknowledges ...nancial support from the Belgian Federal Government (PAI grant P6/07 Economic Policy and Finance in the Global Equilibrium Analysis and Social Evaluation) and the TOM (Transnationality of Migrants) Marie-Curie research and training network. The ...ndings, conclusions and views expressed are entirely those of the authors and should not be attributed to the World Bank, its executive directors or the countries they represent.

<mark>1</mark>
"On the day I left Nigeria, I felt sad because I was leaving my family behind. I believed I would return eight years later, probably marry an Igbo girl, and then spend the rest of my life in Nigeria But 25 years ago, I fell in love with an American girl, married her three years later, and became eligible to sponsor a Green Card visa for my 35 closest relatives, including my parents and all my siblings, nieces and nephews. The story of how I brought 35 people to the United States exempli...es how 10 million skilled people have emigrated out of Africa during the past 30 years. We came to the United States on student visas and then changed our status to become permanent residents and then naturalized citizens Our new citizenship status helped us sponsor relatives, and also inspired our friends to immigrate here." (Philip Emeagwali)<sup>1</sup>

# 1 Introduction

Diasporas constitute invisible nations that reside outside their origin countries. In 2000, there were over 6 million Mexicans working in the United States, more than 1.2 million Turks in Germany and more than 0.5 million Algerians in France. In relative terms, 45 percent of the Surinamese-born were in the Netherlands; about 35 percent of the native-born from Grenada were in the United States; over 25 percent of Samoans were in New Zealand. Despite some of these staggering numbers, migrant diasporas exhibit diverse patterns, especially in terms of their human capital and education levels. Only 6.5 percent of the 22,000 Angolans in Portugal have post-secondary education whereas this proportion rises to 80 percent among the 715 Angolans in Canada. In total, 90 percent of all Angolan migrants with post-secondary education live in just ...ve destination countries in the OECD.

This paper explores the role of existing diasporas on the size, educational structure and concentration of migration ‡ows across di¤erent destinations. Understanding the role of migrant diasporas, especially how that role interacts with governments’ migration policies is a critical issue for both sending and receiving countries. In addition to the welfare of its citizens living under other countries’jurisdiction, sending countries’governments are concerned about the costs and bene...ts of migration on the residents who stay at home. For the receiving countries, migrants generate signi...cant externalities on the natives through capital and labor markets and as well public

> 1Extract of the keynote speech by Philip Emeagwali at the Pan African Conference on Brain Drain, Elsah, Illinois on October 24, 2003. Philip Emeagwali won the 1989 Gordon Bell Prize, which has been called "supercomputing’s Nobel Prize", for inventing a formula that allows computers to perform their fastest computations - a discovery that inspired the reinvention of supercomputers. He was extolled by then U.S. President Bill Clinton as "one of the great minds of the Information Age" and described by CNN as "a Father of the Internet". He is the most searched-for scientist on the Internet.

2
...nance channels (see Borjas, 1994, 1995, 1999, Razin and Sadka, 2004, Friedberg and Hunt, 1995, among others). In short, regardless of the question at hand, diasporas in‡uence the welfare of all parties concerned - families back at home in the origin country, potential migrants searching for better opportunities and the natives in the destination country.

A large literature in sociology and economics has identi...ed that migrants’networks facilitate further migration of people, movement of goods, capital, and ideas across national borders (see Rauch and Casella, 1998, Rauch and Trindade, 2002, Munshi, 2003, Rauch, 2003, Gao, 2003, Rapoport and Kugler, 2006, Docquier and Lodigiani, 2008). As it is presented repeatedly in the literature, the structure and the size of migration ‡ows arise from a complex mix of self-selection factors (wage di¤erentials, probability to ...nd a job, welfare programs and amenities, migration costs, etc.) and out-selection factors (immigration policies at destination, mobility agreements, etc.). Our contribution is to show the role played by existing diasporas in shaping various characteristics of these ‡ows.

Several studies focused on the self-selection mechanism, generally disregarding network externalities. Extending Roy’s model (see Roy, 1951), Borjas (1987) demonstrate that migrants from poor countries with high returns to skills tend to be negatively selected, thus explaining how changes in the origin mix of US immigrants (from EU countries to Latin American and Asian countries) over time has a¤ected their average skills and performance in the US labor market. Assuming that migration costs decrease with educational attainment, Chiquiar and Hanson (2005) develop a model compatible with positive, negative and intermediate selections, depending on the range of the schooling distribution. They ...nd that Mexican emigrants, while much less educated than U.S. natives, are on average more educated than residents of Mexico and tend to occupy the middle and upper portions of Mexico’s wage distribution. In terms of observable skills, there is intermediate or positive selection of immigrants from Mexico.

Existing migrant networks play an important role on the migration decisions of potential migrants. Relying on the informational and ...nancial support provided by the network, newcomers can lower their migration and assimilation costs. As discussed in Massey et al. (1993), models of migrant diasporas are based on the theory of ‘network externalities’. In particular, Carrington, Detragiache and Vishwanath (1996) show that when moving costs decrease with the size of the network already settled in the destination (an assumption which is supported by many sociological studies), migration occurs gradually over time. Migration tends to follow geographical, cultural or political channels and low-moving-cost individuals migrate ...rst. Their presence lowers the migration costs of the next group and the process continues as long as bene...ts exceed costs of migration<sup>2</sup> . In addition to these cost-based network externalities, diasporas attract new migrants via family reuni...cation programs if the

> 2Pedersen, Pytlikova and Smith (2008) also ...nd evidence of strong network e¤ects in immigration ‡ows into 27 OECD countries during the period 1990-2000

3
destination country government has implemented them. In most continental European countries, family reuni...cation is the main route for many potential migrants. Even in one of the most selective country such as Canada, about 40 percent of immigrants come under the family reuni...cation and refugee programs, rather than selective employment or skill-based programs. Emegwali’s quotation perfectly illustrates these channels. Through network e¤ects (“our presence [. . . ] inspired our friends to immigrate here”) and family reuni...cation programs (“I became eligible to sponsor 35 relatives for a Green Card”), existing diasporas positively impact future ‡ows of migrants.

Only a few papers analyze the linkages between diasporas and the structure of migration ‡ows. Building on Chiquiar and Hanson (2005), Mc Kenzie and Rapoport (2007) start from the intermediate selection case (which re‡ects the Mexico-to-US pattern) and demonstrate that a decrease in migration costs generally has a stronger e¤ect on low-skill migration than on high-skilled migration.<sup>3</sup> Using survey data from Mexico, they show that the probability of migration increases with education in communities with low migrant networks, but decreasing with education in communities with high migrant networks. Taking advantage of a recent data set on international migration by educational attainment (see Docquier, Lowell and Marfouk, 2009), our paper generalizes this result by analyzing the role of diaspora size on the educational structure of migration from 195 countries to the 30 OECD countries. Accounting for the usual determinants of migration and correcting for several econometric problems, we show that larger diasporas increase migration ‡ows and lower their average educational level, as expected. To reinforce this result, we analyze the e¤ect of diasporas on the geographic concentration of high-skill and low-skill migrants. We show that diasporas increase the concentration of low-skill migrants relative to high-skilled ones.

Interestingly, diasporas explain a large portion of the variability of migrants’‡ows (71 percent) and selection (47 percent). These percentages capture both network externalities that lower migration costs and the e¤ect of family reuni...cation programs. Thus, without changing the generosity of these family reunion programs, educationbased migrant selection rules are likely to have a moderate impact,especially in countries hosting large diasporas. These results are highly robust to various econometric techniques, accounting for the large proportion of zeros and possible correlation of the network size with unobservable components of the migration ‡ows.

The remainder of the paper is organized as following. Section 2 describes migration data and presents some stylized facts on the size and structure of diaspora and migration ‡ows. Section 3 derives testable predictions from a stylized theoretical model. Econometric issues and empirical results are presented in Sections 4 and 5. Finally, Section 6 concludes.

> 3Bertolini (2009) provides also similar evidence from the Ecuadorian migration to Spain and the US. The negative selection of Ecuadorian migrants to the US is largely explained by the size of the networks at destination.

4
# 2 Stylized facts

The term diaspora (in ancient Greek, "a scattering or sowing of seeds") refers to dispersion of any people or ethnic population, voluntarily or by force, from their traditional homelands and the ensuing developments in their culture in the destination, mostly as a minority. In the economic sense, the diaspora refers to migrants who gather in relatively signi...cant numbers in a particular destination country or region. Some examples are the Turkish Gastarbeiter in Germany, South Asian workers in the Persian Gulf and Cuban migrants in the US.

Following this de...nition, we consider the size of a diaspora as the population (aged 25+) born in country i and living in country j. We use the Docquier, Lowell and Marfouk (2007, referred to as DLM from now on) database which extends and updates Docquier and Marfouk (2006). Based on census and register information on the structure of migrant communities in all OECD countries in 1990 and 2000, DLM database provides the stock of immigrants from any given country in each of the OECD countries by education level. The dataset covers only the adult population aged 25 and over, thus excludes children and students who emigrate temporarily to complete their education. In addition, migration is de...ned on the basis of the country of birth rather than citizenship<sup>4</sup> .

The main strength of the DLM database is that it distinguishes between three levels of education for migrants. High-skilled migrants are those with post-secondary education. Medium-skilled migrants are those with upper-secondary education completed. Low-skilled migrants are those with less than upper-secondary education, including those with lower-secondary and primary education or those who did not go to school. The main characteristics of the diaspora that we consider in this paper are the following:

- The size of the diaspora, measured as the population aged 25+ born in country i and living in the OECD country j (= i).

- The education level of the diaspora, proxied by the log-ratio of the proportions of high-skill to low-skill migrants.

- The concentration of the diaspora, measured as the Her...ndhal index applied to the distribution of the diaspora across di¤erent destinations.

Table 1 shows the 20 largest bilateral migrant communities residing in the OECD countries, both by overall size and by di¤erent education levels. The distinction

> 4Even though this is the standard de...nition of a migrant, especially in the economics literature, the dataset does not include second generation children who are born in the destination country even though they might constitute an important part of a diaspora in the sociological sense. This is simply due to absence of comprehensive administrative data in tracking of the migrants’children. However, we expect diaspora sizes inclusive and exclusive of second generation to be highly correlated.

5
between skilled and unskilled diasporas and its consequences is one of the most important contributions of this paper. With respect to the size, Table 1 allows to observe directly some of the determinants of the size of the diaspora, especially at a given destination country. As clearly seen in Table 1, the sizes of sending and receiving countries’populations are primary determinants of the size of the diasporas. That is why the United States appears as the home to many of the largest migrant communities and larger developing countries (such as Mexico, Turkey, the Philippines and India) are the main sending countries. Other factors, such as wage di¤erentials, physical distance, linguistic proximity, colonial links, immigration policies at destination, are also frequently identi...ed in the empirical literature as determinants of migration and clearly in‡uence the migration corridors listed in Table 1.

In order to shed some preliminary light on how existing networks a¤ect migration ‡ows and and especially their human capital (educational) composition, let us look at the size and the educational structure of the Turkish diaspora in three di¤erent European countries: Germany, Spain and Luxembourg. Turkey is an interesting case since it does not have any colonial links, has no linguistic proximity with any of the major destination countries<sup>5</sup> but has large diasporas in a limited number of countries like Germany (see Table 1). The geodesic distance between Turkey and the three considered European countries is broadly the same and wage levels at destination are not very di¤erent across destination countries (they are higher in Luxembourg and lower in Spain). The data on the size of diaspora and the educational structure of those diasporas display striking di¤erences. In 2000, there were only 194 Turkish migrants in Luxembourg, with 44% (26%) with a tertiary (primary) education level. In Germany, the corresponding ...gures are 1.2 million Turkish migrants with 6% (86%) with a tertiary (primary) educational level. In Spain, there were 1,040 Turkish migrants, with 33% (29%) with a tertiary (primary) educational level. This simple example highlights the striking relationship between migrants’networks and both the size and the skill composition of migration ‡ows.

What is the extent of the relationship between diasporas and migration ‡ows and how general is it in the data? Figure 1 provides another perspective and depicts the size of bilateral diasporas and the proportion of post-secondary educated (highskilled) from four origin countries: Mexico, Morocco, Algeria, Mauritania. The curves are the exponential trends estimated for all origin countries and show that there is negative relationship between the diaspora size and the level of education. This ...gure shows the importance of analyzing bilateral data with econometric models that account for origin and destination country speci...c e¤ects.

The next question is on the concentration/dispersion of migrants across di¤erent destinations. Figure 2 compares the concentration index (measured by the Her...ndhal’s index) of high-skill and low-skill migrants and indicates that there is a positive relationship between the two. In other words, for many source countries, both the

> 5Turkish is an Ural-Altaic language. The only European languages that are grammatically close are Finnish and Hungarian but they have almost no common vocabulary.

6
high and low skilled migrants tend to be either concentrated in few destination countries or relatively dispersed across the globe. A closer look also reveals that a larger share of the observations lie below the 45-degree line on the right side of the ...gure indicating low-skill migrants are even more concentrated than high-skilled migrants if the overall migration is concentrated. On the other hand, more observations on the left side of the ...gure are above the 45-degree line implying high-skill migrants are more concentrated if the overall concentration level is low. Another contribution of the paper is to empirically identify the determinants of the relative concentration (skilled vs unskilled) of the diasporas.

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|Size|4,454,823|1,097,000<br>493,459<br>430,941<br>393,157<br>367,000<br>336,375<br>330,418<br>330,380<br>310,608<br>280,422<br>275,017<br>267,219<br>218,124<br>211,172<br>206,460<br>200,665<br>191,764<br>190,578<br>178,551||
|---|---|---|---|
|skilled diasporas<br>Destination|Un. States|Germany<br>France<br>France<br>Un. States<br>Germany<br>France<br>Un. States<br>France<br>Un. States<br>Un. States<br>Un. States<br>France<br>Un. States<br>Turkey<br>Un. States<br>Canada<br>Australia<br>Poland<br>Un. Kingdom||
|Low <br>Origin|Mexico|Turkey<br>Portugal<br>Algeria<br>El Salvador<br>Italy<br>Morocco<br>Cuba<br>Italy<br>Vietnam<br>China<br>Dom. Rep.<br>Spain<br>Guatemala<br>Bulgaria<br>Italy<br>Italy<br>Un. Kingdom<br>Ukraine<br>India|09)|
|as<br>Size|919,139|833,958<br>664,406<br>439,163<br>437,264<br>434,547<br>418,794<br>387,067<br>381,348<br>365,420<br>347,127<br>307,541<br>220,280<br>202,300<br>199,321<br>184,472<br>182,300<br>174,043<br>156,984<br>154,960|arfouk (20|
|killed diaspor<br>Destination|Un. States|Un. States<br>Un. States<br>Un. States<br>Un. States<br>Un. States<br>Un. States<br>Un. States<br>Australia<br>Canada<br>Un. States<br>Un. States<br>Un. States<br>Un. States<br>Un. States<br>Un. States<br>Un. States<br>Un. States<br>Un. States<br>Canada|Lowell and M|
|Highly s<br>Origin|Mexico|Philippines<br>India<br>Canada<br>Korea<br>China<br>Un. Kingdom<br>Germany<br>Un. Kingdom<br>Un. Kingdom<br>Vietnam<br>Cuba<br>Taiwan<br>Japan<br>Jamaica<br>Colombia<br>Poland<br>Iran<br>Russia<br>Philippines|urce: Docquier,|
|Size|6,374,825|1,272,000<br>1,163,555<br>969,004<br>841,699<br>836,780<br>807,305<br>803,500<br>715,825<br>676,640<br>646,815<br>637,584<br>619,185<br>580,250<br>536,236<br>527,520<br>512,778<br>461,085<br>456,000<br>449,795|So|
|al diasporas<br>Destination|Un. States|Germany<br>Un. States<br>Australia<br>Un. States<br>Un. States<br>Un. States<br>Un. States<br>Un. States<br>Un. States<br>Un. States<br>Un. States<br>Un. States<br>Canada<br>France<br>Un. States<br>France<br>Un. States<br>Germany<br>Un. States||
|Tot<br>Origin|Mexico|Turkey<br>Philippines<br>Un. Kingdom<br>China<br>India<br>Vietnam<br>Cuba<br>Canada<br>Korea<br>Germany<br>Un. Kingdom<br>El Salvador<br>Un. Kingdom<br>Portugal<br>Dom. Rep.<br>Algeria<br>Italy<br>Italy<br>Jamaica||

8
<!-- Start of picture text --> 1,0 |<br>0.9 a<br>,<br>0.8 *<br>* .<br>0.7 *<br>Ree ..<br>2<br>0.6 “3 >*<br>s ?<br>0,5 *s e °<br>. *<br>0.4 s . ¥ 2] ‘ .<br>* .<br>7? .<br>0,3 o¢<br>as » Lal ad<br>0,2 a ae ?<br>0.1 a a $ . a a nd e »* +<br>a "s<br>0,0 —- ——— —Sj = r ———<br>4 6 8 10 12 14 16<br>* Mexico = Morocco * Algeria 4 Mauritania<br>—-Expon. (Mexico) —-Expon. (Morocco) —-Expon. (Algeria) —-Expon. (Mauritania) |<br>hi Sk i eee = a egTe aR yO eeoe =.<br>10 *<br>0,9 x Ke *<br>*<br>_ 08 * x ® ae“<br>Fy 1 * ¥<br>= 07 y v<br>32: 0.6 *2 Xx*dee * « ‘<br>E;> 0 Le = 2 * * *<br>§ ”‘ 7%» * oe. : tt<br>= 04 * pa as - tL: ss ”<br>3z *x EX* oyOm giles Se Kine9 gene Rin ee se ** 4<br>ea = * * i 2 my x * oh<br>g * Paty! es os<br>0.2 wy he wx * ¥<br>x * Ay *ex z = 1<br>01<br>004<br>0,0 01 0.2 03 04 0,5 0,6 67 08 09 10<br>Concentration index oflow skilled migrants<br><!-- End of picture text -->
# 3 Theoretical foundations

We consider model of migration with a single skill type in order to model the e¤ects of diasporas. A worker endowed with h units of human capital earns a wage wih in country i where wi is the skill price in that country. As in Rosenzweig (2008), this structure re‡ects the assumptions that (i) the main source of variation in wages within a country is the di¤erences in the human capital levels (h) of the residents and (ii) the source of variation in wages across countries is the di¤erences in average skill levels and skill prices (wi). The individual utility is linear in income but also depends on possible moving costs and characteristics of the country of residence. The utility of a type-h individual born in country i and staying in country i is given by: where Ai denotes country i’s characteristics (amenities, public expenditures, climate, etc.) and "i is a iid extreme-value distributed random term. The utility obtained when the same person migrates to country j is given by The migration costs are divided into two categories. Cij captures moving and assimilation costs that are borne by the migrant. These would include transportation costs, expenditures to learn the new language, ...nd a job and obtain necessary licences to practice a profession etc. Vij represents policy induced costs borne by the migrant to overcome the legal hurdles set by the destination country’s government’s policies. These costs include visa fees, the bureaucratic barriers for citizenship or even the amount paid to smugglers above the normal cost of transportation when legal entry is restricted. For simpli...cation, we slightly abuse the terminology and refer to Cij as migration costs and to Vij as visa costs. They both depend on the existing diaspora networks and human capital level of the migrant as explained below. The main motivation to di¤erentiate between these two types of costs is to identify the role of government’s policy on migration ‡ows and characteristics.

Let Ni denote the size of the native population that is within migration age in country i. When the random term follows an iid extreme-value distribution, we can apply the results in McFadden (1974) to write the probability that a type-h individual born in country i will move to country j as Similarly, the ratio of emigrants in country j to residents (Nij=Nii) is given by the following expression
or, in logs, The ratio of immigrants to di¤erent destinations (Nij=Nik) or migrants to the same destination with di¤erent human capital levels may be expressed using similar expressions.

Migration costs, Cij, depend on factors such as physical distance (di;j), destination and origin countries’social, cultural and linguistic characteristics (xi; yj) as well as human capital level (h) of the migrant and the size of the diaspora abroad (Mi;j). Thus, we write Distance has a negative e¤ect on migration so c0d<sup>>0.Becausesocialnetworks</sup> lower information, assimilation and adaptation costs, diaspora has a positive e¤ect on migration and lowering of costs so c0M<sup>< 0.The assumption c</sup> 0h<sup>< 0 captures the facts</sup> that skilled migrants are better informed than the unskilled, have higher capacity to assimilate or have more adaptive skills and, thus, face lower migration costs. Finally, we assume that the advantages of being skilled are likely to be more important when the diaspora size is small and migrants can not rely on others. When the diaspora 00 size is larger, the cost advantages of being skilled decline, i.e. chM<sup>> 0.6</sup> The legal (or the visa) costs, Vij, are determined by the destination country j’s government’s policies and depend on various factors. These policies can be speci...c to sending country i or depend on individual characteristics of the migrants. Many destination countries have speci...c programs for family reuni...cation or for highly skilled individuals. Other countries sign bilateral free mobility agreements or grant automatic citizenship based on colonial links, common ethnicity or religion. The green card lottery program of the US, for example, has country-speci...c quotas.

Diasporas a¤ect the visa costs mainly through family reuni...cation programs. Let fj denote the generosity of the family reuni...cation program of country j which generally does not discriminate between di¤erent origin countries. The probability that a potential migrant from country i has a relative in country j is an increasing function of Mij=Ni. Thus, the overall e¤ect of reuni...cation programs on visa costs depends on the expression<sup><u>fj</u></sup> N<sup>M</sup> i<sup>ij.</sup> The migrant’s human capital level also a¤ects the visa costs if there are selective immigration programs such as the H1-B program in the US. We denote the generosity of economic migration programs as ej and the overall e¤ect of human capital on visa costs depends on ejh. Finally, we formalize the presence of free mobility agreements (such as those between EU members) through a dummy variable bij which is equal

> 6Analyzing the Mexican migration to the US, Mc Kenzie and Rapoport (2007) provide evidence that the decrease in migration costs due to the network e¤ect is stronger for low skilled migrants.

11
to one if an agreement exists. As a result, we de...ne visa costs as Policy variables, fj and ej, only matter for origin countries that do not have free mobility agreements with country j (when bij = 0). The partial derivatives of v(:) with respect to both of the arguments are negative, vf0<sup><0; v</sup> e0<sup><0,v</sup> ff00<sup>; v</sup> ee00<sup>?0and</sup> 00 vef<sup>(:)>0:theprobabilitythatanindividualreliesonfamilyreunionprogramde-</sup> creases (resp. increases) when economic program becomes more (resp. less) generous or vice versa.

The net e¤ect of human capital level on visa costs is given by The e¤ect of human capital on visa costs also depend on the size of the diaspora. When the diaspora size is bigger, the probability that a migrant relies on an economic migration program declines and the probability he relies on family reunion programs increases. Hence, we have 00 since v<sup>ispositive.Withthesede...nitionsinplace,wecanwrite(1)as</sup> ef<sup>(:)</sup>

# 3.1 Self-Selection

This simple model and the underlying assumptions allow us to analyze major characteristics of diasporas, especially how the existing diaspora in‡uences the size of migrant ‡ows, their composition in terms of human capital and concentration across di¤erent destinations. Before proceeding to these questions, we ...rst analyze how changes in human capital level in‡uence the migration decision of the individual and the overall migration level. From equation (4), we have
which is positive if �c0h<sup>�(1 �bij)ejv</sup> 20 � <u>fjNMiij</u><sup>; ejh</sup> � > wi � wj<sup>7</sup> . In the case of South-North migration, we have wj > wi and, therefore, above condition always holds. Hence, level of of migration increases with human capital levels and positive selection is observed. Positive selection is even stronger when 0 network e¤ects on moving costs ��ch� are large and when the host country has a selective immigration policy (i.e. ej is large). We should note that positive selection does not imply that there are more skilled emigrants than unskilled emigrants, but the higher-skilled have a higher propensity to migrate. If the proportion of the highlyskilled among natives is low (such as in Africa), there will still be more unskilled than skilled migrants in destination countries. However, the ratio of the skilled to the unskilled will be higher among migrants when compared to natives. For other types of migration (between rich and rich, between poor and poor, or from rich to poor countries), we might have wj � wi < 0. In that case, negative selection could emerge.

# 3.2 Diaspora Externalities

We now turn to diaspora e¤ects on the size and structure of migration ‡ows. First, from (4), a large diaspora in destination j unambiguously increases current migration ‡ows to j from i: The overall impact depends on the e¤ect of networks on migration costs (c0M<sup>)and</sup> on the generosity of family reunion programs (fj) together with the e¤ect on visa costs (vf0<sup>).Second,weshowthatalargerdiasporaincountryjreducethe’positive</sup> selection’of migrants to j from i:

# 3.3 Immigration Policies

What are the implications of these results for immigration policies? Obviously, a more generous immigration policy, both in terms of family reuni...cation and economic immigration programs, at destination increases the size of immigration ‡ows:

> 7In practice, some reported zeros might not re‡ect the actual absence of migrants. Due to con...dentiality and disclosure rules, some statistics o¢ ces report a zero when the diaspora size is lower than a threshold value. We are not able to distinguish these cases from "true" zeros.

13
00 Immigration policies also a¤ect the selection of immigrants. Since vef is positive, stronger emphasis on family reunion programs (higher fj) reduces the quality (i.e. the positive selection) of immigrants: The e¤ect of stronger economic migration programs (higher ej) on the selection of immigrant is somewhat ambiguous since the ...rst term of the expression below is positive and the second term is negative. A close inspection, however, shows that the 00 net e¤ect is likely to be positive unless vee<sup>isstronglynegative.</sup> Our simple model provides many interesting insights and gives rise to many testable predictions. Due to data availability (especially, in the absence of detailed data on bilateral immigration policies), we focus on some important predictions of the empirical section. These can be summarized as follows:

- The e¤ect of diasporas on the migration ‡ows is unambiguously positive. This impact is composed of the reduction of migration costs and visa costs through a stronger family reuni...cation e¤ect. Both e¤ects yield a total positive impact.

- The e¤ect of diasporas on the selection of migrants and the skill ratio is negative. A larger diaspora lowers migration and visa costs for all skill levels but the intensity of reduction is stronger for low-skilled migrants.

- The impact of diasporas on the concentration level should be in line with the e¤ect in terms of selection. In particular, if diasporas tends to bene...t a negative selection process, it should increase the concentration of low-skill migrants compared to the concentration of high-skill migrants.

# 4 Empirical Analysis

In this section, we analyze the determinants of the important characteristics of international migration ‡ows - their size, their educational composition and their relative concentration by education level across di¤erent destination countries. In particular, in line with the theoretical model, we assess the impact of existing diasporas as well as other factors that in‡uence migration ‡ows. We start with OLS regressions but also account for important econometric problems using other techniques. The ...rst important issue is the high proportion of observations with either zero or unde...ned 14
values<sup>8</sup> . The second one is the correlation between the diaspora size and the error term, due to the presence of some unobservable bilateral components that a¤ect both the size of the diaspora and migration ‡ows. One important aspect of the whole analysis is the robustness of the main results to alternative estimation techniques.

# 4.1 Size

The ...rst question we ask is on determinants of migration ‡ows and the role of the diaspora size. In equation (4), the dependent variable is ln [Nij(h)], i.e. the log of the migration ‡ow between 1990 and 2000 from country i to country j of individuals with skill level h. We proxy it by taking the di¤erence of the migration stocks observed in 1990 and 2000.

Among the main determinants of migration ‡ows in equation (4) are the wage differential (speci...c to each skill level), migration costs and the factors in‡uencing visa costs and other legal barriers. In Appendix B, we report the data sources and the way we construct measure the explanatory variables that proxy determinants of migration ‡ows. We have good estimates for skill prices in destination countries (wj) but fairly imprecise data on wages at origin (wi) in order to construct the wage di¤erential variable (wj � wi). One way of resolving this problem is to include origin country dummies �i that capture the combined e¤ect of all unobserved characteristics of the origin country i on the migration ‡ow to country j. These origin country dummies also capture the role of stock of residents with education level h (ln [Nii(h)]) as well all migration costs speci...c to the origin country (xi) in equation (4). Pair-speci...c factors in‡uencing migration costs are captured by geographical distance between the two countries, colonial links (a dummy variable) and linguistic proximity. We also introduce a dummy variable indicating whether the two countries are subject to the Schengen agreement favouring the mobility of persons within the European Community. The set Aj includes destination-speci...c variables that a¤ect the attractiveness of country j in terms of migration such as population sizea and social expenditures as a share of GDP (as a measure of the extent of social welfare). The proxy for selective immigration policies is measured by the share of refugees in immigrants admitted in 1990 by country j. Finally, we capture diaspora e¤ects by size of the diaspora in 1990 and denoted by the variable Mi;j: It should be clear that the estimated impact of Mi;j in the estimation is a combined e¤ect through Cij (network e¤ects that lower migration costs) and the impact on Vij (family reuni...cation e¤ects that lower visa costs).

Introducing these variables, we get a ...rst speci...cation for the migration ‡ow with observable destination speci...c variables: 8 Some reported zeros might not re‡ect the actual absence of migrants. Due to con...dentiality and disclosure rules, some national statistics o¢ ces report zero when the diaspora size is below a threshold level. We are not able to distinguish these cases from "true" zeros.

15
ln [Nij(h)] = �0 + �1 ln (Mij) + �2di;j + �3wj + �4Aj + �i + �ij (10) where ln [Nij(h)]is the change in the migrant stock observed between 1990 and 2000 from country i to country j with education level h, Mij is the size of the diaspora in 1990, di;j is a vector of other observable bilateral variables a¤ecting the migration costs as described above, wj is the level of wages at destination and Aj is a set of other destination speci...c variables thought to a¤ect the attractiveness of country j.

Above speci...cation assumes that the e¤ect of all destination country speci...c variables is well captured by wj and Aj. This is obviously a strong assumption as it is very likely that other factors play a signi...cant role in attracting migrants in country j. In addiition, some variable such as the immigration policy might be measured in an imprecise way. The empirical measurement of immigration policies is a well known challenge in the literature and has so far not received a full satisfying treatment. Since we are mainly interested in estimating the impact of Mij , in the next speci...cation, we introduce destination country dummies �j that capture the combined impact of unobserved characteristics of host countries: Compared to the previous model in (10), introduction of destination country dummies lead to an improvement of the speci...cation and thus can minimize the case of a misspeci...cation bias. Our results in the next section show that insertion of destination ...xed e¤ects leads to an increase in the R<sup>2</sup> by more than 10 percents. This model should thus be preferred, at least as far the estimation of �1 is concerned.<sup>9</sup>

# 4.2 Selection

We use the selection ratio, the number of skilled over unskilled migrants, as the proxy for educational (or the human capital) structure of migration ‡ows and diasporas. It is de...ned as S = Mij <u>(s)</u><sup>whereMij(s)andMij(u)refertothenumberofskilled</sup> ij Mij (u)<sup>,</sup> and unskilled migrants respectively. In line with Grogger and Hanson (2008) and the original de...nition in Docquier, Lowell and Marfouk (2007), we de...ne skilled and unskilled migrants as migrants with post-secondary and primary education levels, respectively . Equation (4) can be manipulated to be written in terms of the ratio of di¤erent skill levels to the same destination as a result of the extreme-value assumption of the error term. Depending on the introduction of destination dummies or not, the estimated equations are :

> 9Of course, the cost of adopting speci...cation (11) is that, we can not estimate the impact of destination speci...c variables such as the wage levels wj in host countries. Please refer to Rosenzweig (2008) and Grogger and Hanson (2008) for a discussion.

16
and The availability of data for 1990 also allows us to study the impact of diaspora on the change in the selection ratio (which is broadly equal to the selection ratio of new migrants). The two estimated speci...cations are then obtained by substituting ln(Sij) by its change between 1990 and 2000, �ln(Sij).

# 4.3 Relative Concentration

We also explore the relative concentration of diasporas across education levels. In particular, we ask whether diasporas tend to lead to more concentration of unskilled rather than skilled migrants at a given destination. We construct our destinationspeci...c relative concentration measure as the following: where indices s and u refer to skilled and unskilled migrants. A nice property of this bilateral measure is that its sum across destination countries j boils down to the di¤erence between Her...ndhal indices for skilled and unskilled migrants.

Once again, we consider regression models with and without destination dummies and consider regression on levels (relative concentration Cij<sup>s�C</sup> ij<sup>uobservedin2000)</sup> and on change between 1990 and 2000. The models for the levels are: and The speci...cations relative to the changes are obtained by substituting Cij<sup>s�C</sup> ij<sup>u</sup> relative to 2000 by �(Cij<sup>s�C</sup> ij<sup>u) where �refers to the change between 1990 and 2000.</sup> The latter speci...cation is particularly demanding since the dependent measures "a di¤erence in di¤erences" of concentration rates.

# 4.4 Econometric Issues

The estimation of models (10-15) entails several econometric challenges that might lead the estimation of those models by OLS to generate inconsistent estimates. There are two basic reasons. The ...rst one is related to the occurrence of zero or unde...ned values for the dependent variables in a large portion of the observations. The second one is the potential correlation of ln(Mij) with �ij due to the presence of an unobservable component a¤ecting the size of the diasporas and the characteristics of new migrants. We now discuss how we address these issues.

17
# 4.4.1 Zero or unde...ned values for dependent variables

One of the most important features of our dataset is the high proportion of zero observations either for the size of diasporas in 2000 or for the ‡ows of migrants between 1990 and 2000. This naturally occurs in many migration datasets as there is almost none or minimal migration for many country pairs. Pooling the data across the two periods, we have zero values in about 31% of the observations for the stock of migrants and in around 36% for the ‡ows.

Our model is fully consistent with such large number of zero observations. Predicting a continuous number of emigrants, our model is an approximation of the "discrete-number" real world with Nij(h) 2 N. If ln [Nij(h)] < 0, less than one migrant wants to leave her country<sup>10</sup> . This means that the bilateral migration ‡ow is nil. The probability that Ni;j(h) = 0 is This case might arise for a number of reasons such as low wage di¤erentials, large distances, high migration or visa costs. In turn, those latter costs obviously depend on the size of the existing diaspora.

Large number of zero observations occurs frequently in other empirical studies in international economics such as gravity equations in trade models. In the estimation of models (10-11) by OLS for the size of migration ‡ows, the high occurance of zero values is likely to lead to inconsistent estimates. The use of a log speci...cation drops the zero observations from the sample which is likely to result in biased estimates of the impact of diasporas and other variables on the migration ‡ows and their selection. For instance, it might be the case that there are no migrants from country i to country j because migration costs are too high. In turn, migration costs might be too high because distance is too high and there is no diaspora. In this case, the exclusion of those observations leads to underestimation of the impact of the variables a¤ecting the migration costs such as distance, colonial links, linguistic similarities or diasporas.

The ...rst alternative is to use Poisson regression models that relies on pseudo maximum likelihood estimates, as advocated by Santos Silva and Tenreyro (2006) who show that the use of log linearization for gravity models leads to inconsistent estimates of the coe¢ cients (such as the one relative to distance). A ...rst reason, as mentioned before, is the exclusion of zero observations for the dependent variable. A second reason is that the expected value of the error will depend on the covariates of the model and hence will lead to estimation biases of the coe¢ cient. In order to address that, we carry out Poisson regressions of the models explaining the size of the migration ‡ows (i.e. models 10-11). The Poisson solution is nevertheless unfeasible for the selection and the concentration analyses. For the selection, the existence of

> 10In practice, some reported zeros might not re‡ect the actual absence of migrants. Due to con...dentiality and disclosure rules, some statistics o¢ ces report a zero when the diaspora size is lower than a threshold value. We are not able to distinguish these cases from "true" zeros.

18
zero values for Mi;j(h) leads to unde...ned values for Sij, which cannot be handled by the Poisson approach.<sup>11</sup> For the concentration regressions, we end up with many negative values (more concentration for the unskilled compared to the skilled), which precludes the use of Poisson regression since they are count data models.<sup>12</sup> A second alternative involves techniques accounting explicitly for a potential selection bias by two-step Heckman regression. In general, for all the features that we analyze (migration ‡ows, selection and relative concentration), the ...rst step involves the estimation of a selection equation - the probability for a given country pair to have a positive migration ‡ow.<sup>13</sup> The usual procedure implies the use of an instrument in the probit equation, i.e. a bilateral variable that in‡uences the probability of observing a diaspora between the two countries but does not in‡uence the size of this diaspora.

It is di¢ cult to ...nd such an instrument but one possible candidate is diplomatic representation of the destination country in the origin country. Diplomatic representation might a¤ect the probability of having at least one migrant by setting some kind of threshold on the initial migration and visa costs faced by potential migrants. In the absence of any diplomatic representation of country j in country i, the cost to get a visa can simply be too high so that nobody would consider to migrate to country j: The role of diplomatic representation in the migration process is to a certain extent analogous to the role played by a common religion for trade relationships. As argued by Helpman et al.(2007), a common religion (a proxy of costs of establishing business linkages) a¤ects the extensive margin of trade (i.e. the probability of export) but not the intensive margin (i.e. trade volumes). In regressions (10-13), the use of a two-step Heckman approach yields intuitive results both for the ‡ow and for the selection equation. In particular, for the selection equation, we ...nd that diplomatic

> 11Strictly speaking, the estimation of models (12-13) leaves out a set of observations for two reasons. The main reason is that the selection ratio is unde...ned due to the fact that Mij(u) = 0; i.e. the size of the unskilled diaspora is equal to zero. Poolling the data across the time periods, the fact that there is no unskilled diaspora leads to the exclusion of 35.7% of the observation. A second minor reason is that the use of the log of the skill ratio leaves out observations for which we observed Mij(s) = 0 and Mij(u) > 0; i.e. a diaspora with some unskilled migrants but no skilled migrants. The log transformation leads to a further exclusion of 256 pairs of countries (for 1990 and 2000), i.e. to an additional exclusion of 2.1% of the total observations.

> 12For the relative concentration, we could include in the OLS regressions zero values. Nevertheless, in order to have consistent subsamples with the analysis of selection and size, we consider a subsample of pairs for which we have non zero values for Cij<sup>s�C</sup> ij<sup>u:Thesezerovaluesareexclusivelyrelatedto</sup> zero values for both concentration indexes , i.e. correspond to Cij<sup>s= 0andC</sup> ij<sup>u= 0:Inotherwords,</sup> we have no case for which concentration levels would be positive and exactly similar between skilled and unskilled.

> 13To be more precise, for the analysis of migration stock, the probability that a given observation will be included in the regression is directly related to the probability of observing a diaspora (either regardless of the skill level, either for a particular skill level) for this country pair. For the migration ‡ows, the probability is exactly the same since we have no case of zero migration ‡ow with positive values of the stock in 1990 and 2000. For the analysis of selection, the probability is related to the existence of a diaspora or at least a skilled diaspora.

19
representation of country j in county i tends to positively a¤ect the probability of observing a diaspora of country i in country j. Furthermore, the mills ratio turns out to be signi...cant in the ‡ow equation, suggesting that accounting for a selection bias is important.

Since the observed level of diaspora in 1990 is used as a regressor, the use of diplomatic representation leads to some collinarity problems in the selection equation. In order to mitigate the collinearity problems, it is possible to run Heckman two-step regressions without any additional instrument. As stressed by Wooldridge (2002), the use of an additional instrument in the probit equation is not strictly necessary. The drawback of not using an additional instrument is that the Mills ratio might become highly collinear with the explanatory variables of the ‡ow equation, which in turn lowers the signi...cance of the coe¢ cients. This is not the case for most of our regressions. This method will therefore be used in the benchmark regressions. Nevertheless, as a robustness check, we carry out the same regressions using diplomatic representation as an instrument (Appendix A).

# 4.4.2 Correlated unobservables with the diaspora

One issue in identifying and estimating endogenous social e¤ects (like the network e¤ects in this paper) is the presence of unobservable correlated e¤ects as explained by Manski (1993). In our framework, it could be the case that unobservable bilateral components a¤ect the size of the diaspora Mij and the dependent variables. For instance, unobserved cultural proximity between country i and country j might a¤ect simultaneously the stock of migrants, the current ‡ows of new migrants and their selection. The cross-sectional nature of the data prevents us to estimate directly those unobservable components. Therefore, those e¤ects will be included in the error term, which in turn leads to some kind of omitted variable bias and to some correlation between M and the error term. ij We follow Munshi (2003) and proceed to a variable instrumental estimation of model (11) and (13) in order to address this issue and check the robustness of the results. In each case, we consider two instruments, i.e. variables correlated with Mij but uncorrelated with the migration ‡ows or the selection ratio. The use of two instruments allows us to check the empirical validity of this second condition through Hansen over-identi...cation tests. Our ...rst instrument is a dummy variable capturing whether the two countries were subject to a temporary guest worker agreement in the 1960s and 1970s. One can expect those guest worker agreements to exert a strong impact on the initial formation of a stock of migrants in the 1960s and the 1970s, hence in‡uencing the stock in 1990. In contrast, it is unclear why those initial agreements would in‡uence the contemporaneous migration ‡ows beyond the impact exerted by the diaspora itself. Examples of such a process are illustrated by the impact of the post-war guest worker agreements between Belgium and Italy or Spain. The second instrument is a variable capturing the unobserved diaspora in the 20
1960s 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. The basic measure is IVij � ln(popi � immstj=distij) � confli where popi is the population size in the 1960s of country i, immstj is the immigration stock of country j in the 1960s, distij is the distance between i and j and confli is a dummy variable capturing the occurrence of armed con‡icts in country i during the 1960s.

Our instrument should be correlated with the size of the diaspora observed in 1990. The variable popi is used as a proxy for the size of potential migrants in sending country i while immstj is a proxy of the openness and the size of the receiving country j in the 1960s. The product of the two is divided by the distance between the two countries captures the size of migration costs. This variable is multiplied by the con‡ict variable speci...c to the sending country to capture push factors causing people to leave country i. If this last variable is not correlated too much over time, this should impact the stock of migrants in the 1960s but not the ‡ows of migrants coming from country i in subsequent periods such as the 1990-2000 period. In other terms, the low degree of serial correlation in the confl variable ensures that our IVij variable is uncorrelated with our dependent variable, as the usual over identi...cation test supports the exclusion restriction.

We only consider con‡icts observed between 1946 and 1960 in order to capture push-factors leading to emigration in the 1950s and 1960s. We distinguish minor con‡icts (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. We ...rst use CONFL1; then we use CONFL2 and ...nally we add up the two variables. F-stat statistics of ...rst stage regressions show that the correlation between this instrument set and the diaspora is relatively high. The results of the Hansen over-identi...cation test suggest furthermore that the second condition of no correlation between the instrument set and the error term is supported by the data.

# 5 Estimation Results

## 5.1 Impact on Flows

Table 2 presents the estimation results regarding the determinants of migration ‡ows and especially the role of diasporas. Columns (1) through (4) report the results on aggregate ‡ows while columns (5) through (8) give the results for low-skilled and highskilled migration ‡ows. The OLS estimates of equations (10) and (11) are presented in columns (1) and (2) where a signi...cant number of observations with zero migration ‡ows (and the size of the diaspora in 1990) are dropped. Columns (3) through (8) report the results from the two-step Heckman approach where the regressions without additional instruments are used as the benchmark.

21
In appendix A, we check the robustness of the results presented in Table 2. Table A1 presents the coe¢ cients obtained with using diplomatic representation as an additional instrument in the Heckman regressions. Table A2 presents the results of the Poisson regressions. As expected, we ...nd that diplomatic representation signi...cantly increases the probability of having a diaspora at destination, re‡ected by the positive and signi...cant coe¢ cient in the selection equation. In all Heckman regressions, the Mills ratio is statistically signi...cant, which suggests that dealing with the large number of zero observations is important. However a comparison of the results in Table 2 with those in Tables A1 and A2 reveals that the estimated coe¢ cient of the lagged diaspora variable is strikingly robust across estimation methods. Therefore, we focus on Table 2 in discussing the implications of our results.

Migration costs, as captured by bilateral distance and linguistic proximity variables, are found to exert signi...cant e¤ects on the migration ‡ows whereas Schengen agreement seems to favor migration of highly skilled workers. Besides those predictable results, the e¤ect of diasporas on the migration ‡ows is quite important with a positive and signi...cant coe¢ cient. In the case with both destination and origin dummies, this coe¢ cient lies between 0.62 and 0.77. Note that the speci...cation used in (10-11) is similar to that of a �-convergence model. A positive coe¢ cient for the lagged diaspora implies that there is no sign of convergence in the size of bilateral stocks of migrants, even when controlling for country ...xed e¤ects (capturing populations, individual domestic policies and economic conditions that in‡uence incentives to migrate). This is probably due to the fact that migration to the North, especially from the South, sharply increased during the nineties. Since our period of interest is 1990-2000, our results clearly illustrate that country pairs with large initial diasporas exhibit higher growth rates compared to pairs with smaller diasporas.

As expected, OLS leads to an underestimated coe¢ cient due to the exclusion of zero observations and the related selection bias. Methods that account for those zero values lead to slightly higher estimates. The estimated coe¢ cient is almost the same in the Heckman two-step and Poisson regressions, emphasizing the robustness of the results. It is also quite similar whether we include an instrument in the selection equation of the two-step Heckman approach (Table A1)<sup>14</sup> .

> 14With diplomatic representation used as an instrument in the selection equation, we get a coef...cient of 0.660 for the impact of diaspora instead of 0.699 in the benchmark regressions. Note that the di¤erence is not exclusively due to the estimation method since the use of diplomatic representation causes a loss of additional observations (190 origin countries instead of 195 in the benchmark regressions).

22
||(8)<br>High-skill<br>0.728<br>(28.29)***<br>-0.023<br>(0.16)<br>1.373<br>(13.22)***<br>0.004<br>(0.08)<br>0.493<br>(2.71)***<br>-0.338<br>(3.33)***<br>0.236<br>(6.98)***<br>0.033<br>(7.51)***<br>0.069<br>(9.32)***<br>-6.701|(6.32)***|
|---|---|---|
|:|(7)<br>High-skill<br>0.625<br>(44.57)***<br>0.169<br>(1.72)*<br>0.683<br>(10.29)***<br>-0.341<br>(9.58)***<br>0.598<br>(5.23)***<br>0.196|(0.36)|
|skill level <br>.|(6)<br>Low-skill<br>1.192<br>(6.90)***<br>-1.699<br>(2.05)**<br>1.413<br>(3.23)***<br>0.057<br>(0.31)<br>1.154<br>(1.31)<br>0.015<br>(0.87)<br>2.411<br>(3.22)***<br>-0.131<br>(0.83)<br>-0.020<br>(0.75)<br>-17.084|(2.99)***|
|‡ows by <br>sions (1/2)|(5)<br>Low-skill<br>0.778<br>(22.25)***<br>0.153<br>(0.64)<br>0.322<br>(2.18)**<br>-0.613<br>(7.40)***<br>-0.081<br>(0.28)<br>1.388|(1.20)|
|f migration<br>man regres|(4)<br>Total<br>0.831<br>(23.44)***<br>-0.051<br>(0.29)<br>1.056<br>(8.34)***<br>-0.095<br>(1.63)<br>0.599<br>(2.56)**<br>0.035<br>(6.71)***<br>0.175<br>(1.28)<br>0.109<br>(2.30)**<br>0.040<br>(4.51)***<br>-6.119|(5.07)***|
|rminants o<br> and Heck|(3)<br>Total<br>0.699<br>(43.91)***<br>0.127<br>(1.10)<br>0.496<br>(6.48)***<br>-0.448<br>(10.69)***<br>0.277<br>(2.02)**<br>2.365|(4.02)***|
|le 2. Dete<br>OLS|(2)<br>Total<br>0.616<br>(26.60)***<br>0.278<br>(2.14)**<br>1.026<br>(10.02)***<br>-0.139<br>(2.48)**<br>0.065<br>(0.33)<br>0.035<br>(7.85)***<br>-0.290<br>(2.25)**<br>0.321<br>(9.66)***<br>0.028<br>(3.70)***<br>-4.954|(3.96)***|
|Tab|(1)<br>Total<br>0.620<br>(34.35)***<br>0.331<br>(2.45)**<br>0.388<br>(5.20)***<br>-0.408<br>(9.04)***<br>0.168<br>(1.19)<br>3.750|(6.92)***|
||Lagged diasp<br>Col links<br>language<br>Log(dist)<br>Schengen<br>Immig. pol<br>Social exp<br>Pop at dest<br>Wages at dest<br>Constant||

23
||(8)<br>High-skill|4992|Yes|yes|Heckman|1.11|(8.75)***||
|---|---|---|---|---|---|---|---|---|
|level :|(7)<br>High-skill|5760|Yes|yes|Heckman|1.43|(8.90)***|t 1%|
|s by skill <br> (2/2)|(6)<br>Low-skill|4992|Yes|No|Heckman|1.01|(10.6)***<br>arentheses|igni...cant a|
|ation ‡ow<br>gressions|(5)<br>Low-skill|5760|Yes|yes|Heckman|2.09|(6.70)***<br>atistics in p|at 5%; *** s|
|s of migr<br>ckman re|(4)<br>Total|4992|Yes|No|Heckman|1.92|(7.65)***<br> robust t st|signi...cant|
|terminant<br>LS and He|(3)<br>Total|5760|Yes|yes|Heckman|1.19|(9.35)***<br>ute values of|at 10%; **|
|2. De<br>O|(2)<br>Total|3091|Yes|No|OLS|-|0.76<br>Absol|ni...cant|
|Table|(1)<br>Total|3608|Yes|yes|OLS|-|0.89|* sig|
|||Observations|Dest dum|Orig dum|Method|Mills ratio|R-squared||

24
Extracting the explained partial sum of squares using the results in column (1), we ...nd that diaspora e¤ects explain more than 71% of the observed variability in migration ‡ows and over 80% of the explained variability of the model. This is a rather high level given that the ...t of the regression is quite high, with R<sup>2</sup> amounting to 89%. Columns (5) and (6) report the results for the low-skill migrants while columns (7) and (8) report the results for the high-skill ones. The diaspora e¤ect is higher for low-skill migrants as predicted in our model. This is due to the fact a large diaspora lowers the advantage higher levels of human capital generate in lowering migration and visa costs. The di¤erential impact of diasporas on low-skill migration is again highly robust to alternative speci...cations (i.e. with and without destination country dummies) and to alternative estimation methods. A Wald test on the di¤erence of coe¢ cients of �1 between low and high-skilled migrants (columns 5 and 7) shows that this di¤erence is statistically signi...cant at the 5% level. Note that the e¤ects of distance and linguistic proximity are also higher for low-skilled than for the high-skilled migrants. The latter result re‡ects the fact that linguistic proximity increases the degree of transferability of skills and the ease of entry into the labor market for the low-skilled migrants.

Table 3 presents the instrumental variable estimates of equation (11) with three di¤erent sets of instruments. All sets pass the F-stat test for the strength of instruments and the Hansen J-test of no correlation with the error term at the 5% level. The results of the IV estimation lead to very similar coe¢ cients for the impact of the diaspora on the migration ‡ows. The decrease in signi...cance is mainly caused by the increase in uncertainty due to the instrumentation procedure. Nevertheless, the quantitative and statistical signi...cance of the diaspora remains. Therefore, we conclude that the strong e¤ect of diasporas documented in OLS regressions is robust to the various econometric problems including selection bias and correlation of the diaspora with unobserved factors of the ‡ows.

25
Table 3. Determinants of migration ‡ows : <u>IV estimation</u>

||(1)<br>Total|(2)<br>Total|(3)<br>Total|
|---|---|---|---|
|Lagged diasp|0.761|0.766|0.758|
||(10.92)***|(11.09)***|(10.86)***|
|Col links|-0.051|-0.064|-0.045|
||(0.26)|(0.32)|(0.23)|
|linguage|0.234|0.228|0.236|
||(2.27)**|(2.22)**|(2.29)**|
|Log(dist)|-0.259|-0.253|-0.262|
||(2.84)***|(2.78)***|(2.86)***|
|Schengen|0.160|0.161|0.160|
||(1.11)|(1.11)|(1.11)|
|Constant|2.365|2.306|2.392|
||(2.69)***|(2.64)***|(2.72)***|
|Orig Dum|Yes|Yes|Yes|
|Dest Dum|Yes|Yes|Yes|
|Method|IV|IV|IV|
|F-stat First stage|27.51|26.15|27.29|
|Hansen J-test (p-value)|0.128|0.0640|0.101|
|R2|0.883|0.882|0.883|
|Observations|3486|3486|3486|

Absolute values of robust t statistics in parentheses

* signi...cant at 10%; ** signi...cant at 5%; *** signi...cant at 1%

Instrument sets for Mij in all columns include a dummy for bilateral guest worker agreement and a proxy for diaspora size in 1960. In column (1) , the proxy is computed as ln(popi � immstj=distij) � Conf 1i;In column (2) , the proxy is computed as ln(popi � immstj=distij) � Conf 2i;in column (3), the proxy is computed as ln(popi � immstj=distij) � (conf 1i + Conf 2i):

# 5.2 Impact on Selection

The next question is on the determinants of the selection and the human capital (educational) composition of migrants and the speci...c role of diasporas in this process. Columns (1) to (4) in Table 4 report the results of the estimation of equations (12) and (13) for the skill ratio whereas columns (5) and (6) are estimated for the change in the skill ratio. Columns (1) and (2) are obtained using OLS whereas results in columns (3) to (6) are obtained with the Heckman two-step procedure without instruments.

26
Table 4. Impact of diaspora on selection (ratio high-skill/low-skill) level and change: OLS and Heckman

||(1)<br>Skill ratio|(2)<br>Skill ratio|(3)<br>Skill ratio|(4)<br>Skill ratio|(5)<br>�SR|(6)<br>�SR|
|---|---|---|---|---|---|---|
|Lagged diasp|-0.171<br>(16.19)***|-0.088<br>(8.47)***|-0.194<br>(20.62)***|-0.132<br>(11.83)***|-0.143<br>(17.62)***|-0.108<br>(11.47)***|
|Col. links|-0.042|-0.439|-0.022|-0.410|0.101|0.096|
||(0.62)|(6.08)***|(0.32)|(5.21)***|(1.67)*|(1.46)|
|linguage|0.466<br>(9.38)***|0.703<br>(11.03)***|0.460<br>(9.37)***|0.721<br>(11.68)***|0.176<br>(4.17)***|0.257<br>(4.95)***|
|Log(dist)|0.096<br>(3.35)***|0.273<br>(10.17)***|0.090<br>(3.40)***|0.263<br>(9.96)***|0.086<br>(3.78)***|0.116<br>(5.25)***|
|Schengen|0.502|0.305|0.519|0.303|0.390|0.117|
||(5.65)***|(3.14)***|(6.26)***|(2.97)***|(5.48)***|(1.37)|
|Immig pol||-0.014<br>(4.98)***||-0.015<br>(5.52)***||0.001<br>(0.30)|
|Soc exp||-1.206<br>(16.11)***||-1.253<br>(20.12)***||-0.756<br>(14.42)***|
|Pop. at dest||0.061<br>(3.45)***||0.082<br>(4.58)***||0.056<br>(3.75)***|
|Wage at dest||0.044<br>(9.86)***||0.045<br>(10.47)***||0.035<br>(9.78)***|
|Constant|-1.109|0.002|-0.734|0.257|-1.250|-0.563|
||(1.16)|(0.00)|(1.32)|(0.34)|(2.54)**|(0.87)|
|Dest dum|Yes|No|Yes|No|Yes|No|
|Orig dum|Yes|Yes|Yes|Yes|Yes|Yes|
|Method|OLS|OLS|Heckman|Heckman|Heckman|Heckman|
|Mills|||-0.380|-0.446|-0.10|-0.99|
||||(6.86)***|(7.37)***|(0.22)|(1.88)*|
|Obs|3604|3084|5760|4992|5760|4992|
|R-squared|0.60|0.45|||||

Robust t statistics in parentheses * signi...cant at 10%; ** signi...cant at 5%; *** signi...cant at 1% Results in Table 4 show that the selection of migrants is also in‡uenced by a large set of variables. Bilateral varaibles such as linguistic proximity, distance, the Schengen agreement and wage di¤erentials favor the selection of high-skilled migrants. On the contrary, non-selective immigration policies and generous social expenditures lower the educational mix of the migrants which is in line with the results in Cohen and Razin (2008). More importantly, large diasporas exert a strong negative impact on the skill ratio of migration ‡ows and attract low-skill migrants. Once again, this e¤ect is robust to alternative speci...cations (presence or absence of destination dummies), 27
estimation methods (OLS and Heckman). More importantly, this strong result is maintained when we use the change in the skill ratio between 1990 and 2000 as the dependent variable instead of the level of the skill ratio.

From the results in column (1), we ...nd that diaspora e¤ects explain respectively 47% and 78% of the total and explained variability of the selection ratio in 2000. These numbers suggest that, compared to economic or other selection variables, diaspora e¤ects are rather important. As stated earlier, the diaspora e¤ect is complemetary to the generosity of family reunion programs. The size of the diaspora e¤ect will be smaller in the absence of .reuni...cation programs in the destination country and will be limited to lowering of migration costs through the network effects. These results imply that education-based selective migration policies are likely to have only moderate impact in countries hosting large diasporas unless the extent of family reuni...cation programs are curtailed.

Table 5 reports the results of the IV estimation for the skill ratio of migration ‡ows. Columns (1) through (3) look at the impact on the level of the ratio while Columns (4) through (6) investigate the impact on its change. Similar to the analysis of migration ‡ows, we consider three di¤erent sets of instruments and the IV results con...rm the negative impact of diasporas on the educational composition of migrant ‡ows from the previous table.

# 5.3 Concentration

Our last question is on the determinants of the relative concentration of migrants of di¤erent skill levels and the role diasporas play. The structure of Table 6 is similar to the that of Table 4. Colonial links tend to favor a higher concentration of low-skill migrants compared to high-skill ones, while distance exerts the opposite e¤ect. Once again, diaspora e¤ects are found to be important for explaining the concentration levels and the e¤ect is robust to alternative speci...cations, alternative estimation methods. And the results also hold for the change in the relative concentration index between 1990 and 2000.

28
|timation<br>(6)<br>�LSR<br>-0.212<br>(3.44)***<br>0.270<br>(1.77)*<br>0.235<br>(3.19)***<br>0.019<br>(0.30)<br>0.414<br>(6.08)***<br>-0.481<br>(0.63)<br>Yes<br>Yes<br>IV<br>30.07<br>0.747<br>0.506<br>3486<br> proxy for diaspora<br> (2) , the proxy is<br>d as|
|---|
|): IV es<br>(5)<br>�LSR<br>-0.203<br>(3.22)***<br>0.249<br>(1.61)<br>0.226<br>(3.04)***<br>0.028<br>(0.43)<br>0.415<br>(6.09)***<br>-0.567<br>(0.73)<br>Yes<br>Yes<br>IV<br>29.49<br>0.562<br>0.509<br>3486<br>ents and a<br>i:In column<br>s compute|
|-skill ratio<br>(4)<br>�LSR<br>-0.215<br>(3.50)***<br>0.277<br>(1.82)*<br>0.238<br>(3.24)***<br>0.016<br>(0.25)<br>0.414<br>(6.08)***<br>-0.450<br>(0.59)<br>Yes<br>Yes<br>IV<br>30.16<br>0.574<br>0.506<br>3486<br>theses<br>...cant at 1%<br>rker agreem<br>j)�Conf1<br>the proxy i<br> 2i):|
|diaspora on selection (log high-skill/low<br>(1)<br>(2)<br>(3)<br>Log-skill ratio<br>Log-skill ratio<br>Log-skill ratio<br>-0.218<br>-0.207<br>-0.215<br>(3.01)***<br>(2.78)***<br>(2.95)***<br>0.092<br>0.068<br>0.085<br>(0.52)<br>(0.37)<br>(0.48)<br>0.469<br>0.459<br>0.466<br>(5.41)***<br>(5.20)***<br>(5.37)***<br>0.057<br>0.067<br>0.060<br>(0.75)<br>(0.87)<br>(0.79)<br>0.536<br>0.536<br>0.536<br>(6.38)***<br>(6.38)***<br>(6.38)***<br>-0.468<br>-0.573<br>-0.501<br>(0.42)<br>(0.50)<br>(0.44)<br>Yes<br>Yes<br>Yes<br>Yes<br>Yes<br>Yes<br>IV<br>IV<br>IV<br>30.16<br>29.49<br>30.07<br>0.974<br>0.244<br>0.812<br>0.599<br>0.600<br>0.599<br>3486<br>3486<br>3486<br>Absolute values of robust t statistics in paren<br>igni...cant at 10%; ** signi...cant at 5%; *** signi<br>umns include a dummy for bilateral guest-wo<br>e proxy is computed as ln(popi�immstj=disti<br>opi�immstj=distij)�Conf2i;in column (3), <br>ln(popi�immstj=distij)�(conf1i+Conf|
|Table 5. Impact of <br>Lagged diasp<br>Col links<br>linguage<br>Log(dist)<br>Schengen<br>Constant<br>Orig Dum<br>Dest Dum<br>Method<br>F-stat First stage<br>Hansen J-test (p-value)<br>R2<br>Observations<br>* s<br>Instrument sets for Mij in all col<br>size in 1960. In column (1) , th<br>computed as ln(p|

29
Table 6. Explaining relative concentration between high-skill and low-skill and change in relative concentration

||(1)<br>Rel conc|(2)<br>Rel conc|(3)<br>Rel conc|(4)<br>Rel conc|(5)<br>�RC|(6)<br>�RC|
|---|---|---|---|---|---|---|
|Lagged diasp|-0.502<br>(5.87)***|-0.294<br>(3.54)***|-0.514<br>(9.67)***|-0.347<br>(5.73)***|-0.008<br>(16.05)***|-0.008<br>(15.45)***|
|Col. links|-4.635<br>(4.68)***|-7.085<br>(6.41)***|-4.619<br>(10.69)***|-7.008<br>(14.75)***|-0.040<br>(9.93)***|-0.043<br>(10.45)***|
|Language|0.338|0.373|0.321|0.369|-0.004|-0.005|
||(0.84)|(0.78)|(1.09)|(1.02)|(1.58)|(1.75)*|
|Log(dist)|0.266|0.628|0.269|0.615|0.006|0.006|
||(1.24)|(3.73)***|(1.69)*|(3.91)***|(3.78)***|(4.26)***|
|Schengen|-0.193|-0.076|-0.180|-0.068|0.002|0.001|
||(0.50)|(0.16)|(0.36)|(0.11)|(0.49)|(0.26)|
|Pop. at dest||0.956<br>(7.13)***||0.988<br>(9.33)***||0.003<br>(3.50)***|
|Immig pol||-0.014||-0.013||0.000|
|||(1.31)||(0.84)||(1.51)|
|Soc exp||-1.509||-1.573||0.002|
|||(4.38)***||(4.44)***||(0.52)|
|Wage at dest||0.217<br>(7.69)***||0.217<br>(8.57)***||0.001<br>(4.68)***|
|Constant|5.607|-18.397|-3.240|-10.824|-0.037|-0.111|
||(0.29)|(4.70)***|(1.19)|(2.77)***|(1.60)|(3.33)***|
|Dest dum|Yes|No|Yes|No|Yes|No|
|Orig dum|Yes|Yes|Yes|Yes|Yes|Yes|
|Method|OLS|OLS|Heckman|Heckman|Heckman|Heckman|
|Mills|||-0.405|-0.680|-0.873|-1.684|
||||(1.07)|(1.94)**|(2.44)**|(6.12)***|
|Observations|3920|3367|5730|4966|5730|4966|
|R-squared|0.29|0.17|||||

Robust t statistics in parentheses * signi...cant at 10%; ** signi...cant at 5%; *** signi...cant at 1% 30
# 5.4 Non-linear E¤ects

It is important to explore potential non-linear e¤ects in our econometric speci...cation, especially given the nature of the mechanism through which diasporas are expected to impact the characteristics of migration ‡ows. Two sources of non-linearity can be expected. First, as the size of a diaspora expands, the marginal impact of an additional migrant could decline. Fortunately, the logarithmic speci...cation accounts for this source of non-linearity.

Another potential issue is that diasporas below a certain size could be ine¤ective in lowering migration costs. In other words, smaller diasporas might lead to relatively high search costs for potential migrants, mitigating the positive e¤ects reported in the previous tables. This possibility argues for presence of threshold e¤ects in the impact of diasporas. In order to check the existence of such a threshold, we run rolling regressions of the following type: s s with Xij = Nij or Sij, M<sup>f</sup> ij<sup>s�Max [Mij�</sup><sup><u>M</u></sup> ; 1] and <u>M</u> , the threshold in diaspora size, varying between 0 to 7,500 migrants. Hence, we look at the impact of diasporas on the migration ‡ows and on the migration selection, neutralizing the impact for s diasporas whose size is lower than <u>M</u> . Given the distribution of the diaspora size, we roll over increments of 50 migrants f up to 7,500 migrants. Note that by generating zero values for ln Mij<sup>s</sup> , one should � � f expect the standard error of b�<sup>s</sup> 1<sup>to increase as M</sup> s increases (the variability of ln Mij<sup>s</sup> � � decreases in a nonlinear way). For instance, when <u>M</u> s = 7500, the proportion of zeros f generated for ln Mij<sup>s</sup> becomes higher than 89 percent. The estimation of �b<sup>s</sup> 1<sup>is then</sup> � � based on a very low number of observations<sup>15</sup> . This tends to in‡ate the standard b errors of �<sup>s</sup> 1<sup>.</sup> Figures 3 and 4 plot the evolution of the estimated �b<sup>s</sup> 1<sup>alongwithvaluesof</sup><sup><u>M</u></sup> s with both estimations using Heckman two-step method. Both ...gures suggest that the impact of diasporas is slightly decreasing with the size of diasporas. The evolution over time of the estimated b�<sup>s</sup> 1<sup>’s does not suggest the existence of a minimum threshold</sup> under which diasporas would be ine¢ cient. Consequently, those results are fully consistent with the choice of a double log speci...cation for models (11) and (13) and values of j �b1 j< 1.

> 15Basically, the estimation will only rely on pairs of relatively large sending and receiving countries.

31
Figure 3. Estimating �b<sup>s</sup> 1<sup>withrollingregressions</sup> Dependent = change in diaspora size <!-- Start of picture text --> 0.9<br>0.8<br>0.7<br>0.6<br>0.5<br>0.4<br>0.3<br>0.2<br>0.1<br>0<br>0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000<br>-0.1<br><!-- End of picture text --> Figure 4. Estimating �b<sup>s</sup> 1<sup>withrollingregressions</sup> Dependent = log skill-ratio <!-- Start of picture text --> 0<br>0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000<br>-0.05<br>-0.1<br>-0.15<br>-0.2<br>-0.25<br><!-- End of picture text --> 32
# 6 Conclusion

This paper explores the impact of existing diasporas on the number, skill composition and concentration of international migrants. We ...rst develop a simple theoretical framework emphasizing the role of diasporas which operates through the lowering of both migration costs (due to information and assimilation di¢ culties) and visa costs (due to government policies). Diasporas lower migration costs through network effects and visa costs by increasing the probability of non economic migration through family reuni...cation programs. These two e¤ects increase the size of migration ‡ows and reasonably reduce the selection of high-skill migrants. We then evaluate the implications of the theoretical predictions using new bilateral migration data by educational level. We estimate the role of existing networks in 1990 on the migration ‡ows between 1990 and 2000, on their skill composition and on their relative concentration across educational levels. We account for potential problems related to the nature of the data and check the robustness of initial OLS estimates. First, we abstract from the bias induced by the log linearization of gravity models. Second, we account for the occurrence of a potential selection bias due to the large number of zeros in the country pairs. Third, we take into account a potential endogeneity problem of existing diasporas through instrumental variable estimations. Our results are extremely robust across estimation methods.

In short, we ...nd evidence of a strong impact of existing diasporas. Regarding size, diasporas are by far the most important determinant of migration ‡ows even after accounting for the usual variables a¤ecting bilateral migration costs such as distance, colonial links and linguistic proximity. Extracting the explained partial sum of squares, we ...nd that 71 percent of the observed variability of the migration ‡ows is explained by diaspora e¤ects. Regarding selection, diasporas are found to favor more the migration of the low-skill than migration of the highly skilled. It therefore exerts a strong negative impact on the selection of migrants. We ...nd that diaspora e¤ects explain 47% of the total variability of the selection ratio in 2000. Disregarding diaspora externalities but using much more detailed data on base wages and returns to skill (captured in our ...xed e¤ects), Grogger and Hanson (2008) ...nd that, on average, wage di¤erences explain 58 percent of the immigrant skill gap. This suggests that diaspora e¤ects and wage di¤erences leave little space for education-based selective policies in determining the quantity and quality of immigrants. Our results suggest that policies aiming at increasing the educational quality of the migrants might be highly constrained by the existing migrant’s network. In the presence of large diasporas, more selective migration policies might fail unless family reuni...cation programs are deeply reformed and limited. The same holds for policies that would aim to favor ethnic diversity of the migrants.

33