# Introduction ndividuals make the decision to migrate from their homelands to other countries for various reasons; and migration continues to occur in our present times until it became one of the most prominent problems of the modern era, because there are still many causes that motivate people to leave their home lands and settle somewhere else, no matter that these causes might differ from the previous reasons. The scope of international migration has expanded to involve all societies, especially in developing countries. migration happens in several legal and illegal ways, and thus it may affect many economic and social aspects of the migrant and both of the country of origin and the destination country. Since migration affects the demographics of the country of origin and the destination country, their development path, and their level of growth, there is an urgent need to study migration and understand its aspects and determinants through investigating the causes of this phenomenon, so that decision and policy makers can deal better with it, and find solutions to address the negative effects that it might cause. This study aims to answer these questions: Are the immigration flows responding to the push and pull factors? What is the effectiveness of the determinants in increasing and decreasing the number of immigrants from developing countries? II. # Literature Review International migration and individuals' moving across borders is one of the most important current issues of concern to policymakers, international organizations, and researchers around the world. This issue has been adequately interpreted through theories that focused on the determinants, causes, economic and social implications of migration. "Ravenstein" was the first researcher to write in the field of migration explaining the motives for immigration in 1885; he listed these motives in laws later called the laws of Ravenstein. In 1966 "Lee" improved these laws by focusing on the size of migratory flows and their characteristics. According to Lee: migration depends on the homeland's economy to an extreme extent; Lee acknowledged the existence of push factors that lead to the migration of persons, which are associated with the country of origin, and "pull" factors that attract international migrants to a specific country, in addition to the presence of overlapping obstacles and personal factors connected with the immigration decision. The theory of the neo-classics by Lewis (1954) & Ranis and Fei (1961) explained international and internal migration. According to this theory, migration occurs due to geographical and economic variations affecting the labor market, as countries with abundant employment have lower workers 'wages, while workers' wages increase in capital-intensive countries, which makes the individual think about moving in search of higher wages. This theory assumes that eliminating wage variations could end employment migration. On an individual level, Todaro (1967) believes that individuals plan to emigrate based on their expectations for the cash return, but they must consider the expenses of migration. An immigrant should consider the costs of the trip to another country, and should consider the consequent efforts that will encouner them in searching of a job and adapting to the new work and new language; not to mention the psychological fluctuations related to moving away from family and home (Massey et al., 2011). Many researchers in studying international migration combined the theoretical frameworks and the applied frameworks in attempts to study this phenomenon, its determinants, as well as its effects on economic growth. many studies addressed the phenomenon of international migration by analyzing and researching its motives and effects. (Poot and Cochrance, 2004) conducted a study to measure the economic impact of international migration on New Zealand, they found that migrants affected the economy in both demand and supply; they recommended that future international migration researches should take into account that migratory flows have changed and are not only made for a living, but have become diverse in terms of the composition of migrants, such as skilled labor migration and student flows. While in another study (Bertochi and Strozzii, 2006), investigated the determinants of mass immigration that occurred since the nineteenth century until World War I for fourteen countries (Belgium, Denmark, France, Britain, Germany, Italy, Netherlands, Norway, Portugal, Spain Sweden, Australia, Canada, and America); the results of this study assured that the variances of income and the level of development between countries in addition to the population structure play a prominent role in determining the rate of migration to the countries included in the study sample. In an analytical study on the economic and noneconomic determinants of the international migration of fourteen OECD countries, (Mayda, 2007), has reached annual data for the period from 1980 to 1995; that data indicated that one of the pull factors that attracted immigration is the increase in financial return. On the other hand, the study found that the impact of the "push" factors was not in the individual's share of the total income of the country of origin as expected, but the greatest impact was that of the distance between the country of origin and the destination country, as it had a significant negative impact on international migration. (Mayda, 2010) conducted an applied study on the impact of the economic, social, cultural and demographic determinants of migration on OECD countries, and on measuring the impact of migration on the average income in both sending countries and receiving countries; this study found that obtaining employment opportunities and increasing the average income in receiving countries as well as their less restrictive laws, significantly increase the international immigration rates. Lewer and Van den Berg, 2008, used the gravity model to test the international migration, response to different pull forces. Panel Data covered migration data for 16 OECD countries among all the sending countries of immigrants, for a ten-year period 2008-1991; the results of the analysis of the geographical dimension were not very significant, which indicates the ease of moving across borders for immigrants; on the other hand, it was found that international migration depends on the stock of migrants in the receiving country. Based on the Ageing population and the low birth rates on the European continent, (Ramos and Surinach, 2013) believe that the European Union countries need to import labor from neighboring countries; Ramos and Surinach also analyzed the relationship of bilateral migration with many different factors in the year 2011, by estimating the gravity model of 200 sending countries between 1960 and 2010, this analysis resulted in the size of the population having a positive and important relationship with migration, in addition to the existence of a common language and colonial relationship between receiving and sending countries. Gonzalez and Mesanza, 2011 examined the factors affecting migration of graduate students according to the Erasmus program, they used a sample of Panel Data, from the bilateral flows of the countries participating in the program. Their study showed that the cost of living, the quality of the university, language, and climate were among the most important factors influencing student migration, which amounted to two million in 1987. From the perspective of the sending countries, (Ullah, 2012), chose to study the determinants of labor migration from Bangladesh to 23 countries, during the period 2009-2012, and by using Panel Data, he concluded that economic, demographic and cultural factors had a major impact on labor migration. To call attention to the relationship between economic and political factors in the both origin and host countries, (Westmore, 2014) analyzed data on highly skilled migrants as well as low skilled ones between ninety-two sending and forty-four receiving countries; his findings indicated that high private wages given to skilled labor in the receiving country is linked with the increase in the number of immigrants; these results supported the impact of the differences in policies related to business and labor markets, as the more stringent policies constitute an incentive for highly skilled people to emigrate, while they do not constitute a significant incentive for people with low skills to do so. the study also showed that wage differences were the main driver of migration, especially for high skilled people. As for international migration as an option for individuals driven by several factors at the micro and macro level, the study of (Porumbescu, 2015) added, that the decision to migrate is not only taken at the individual level, but is taken with the participation of all family members; most members work not only to maximize their income, but also to reduce risks that occur as a result of the failure of local markets to allocate resources efficiently. Many economists focus their attention on market defects, such as high rate transactions in the markets as well as limited access to information and weak communication and transportation infrastructure; all this focus creates incentives to send family members away. (Pavkovic et al., 2018) used annual Panel Data for the period 1995-2016, following the Poisson distribution and the "Negative Binomial Regression" model, to study the determinants of migration to 28 European Union countries; these determinants include demographic, economic, social and political variables. the study found that job opportunities and a good standard of living are the two factors that mostly influence the attraction of migrants, which supports the economic incentive for international migration. III. # The Methodology The increased numbers of international migrants to developed countries has imposed itself over the past five decades on all those interested in this phenomenon, and the issue of migration and its impact on various activities in the receiving countries is still drawing intense attention. This obliged academics to work to formulate a model for migration, where international voluntary migration represents a choice for individuals based on specific motivations. (Smith, 2012) believes that it is easy to understand the migration motives on the personal level, but find it hard to study the effects at the country level. Therefore, the Newton Law of Gravity, which is often used to measure trade exchange between countries, has been expanded to include the study of international migration. This model assumes that every country has distinct characteristics (push and pull factors), in addition to the presence of bilateral impacts between countries (factors of distance and common language). However, despite the great interest in the topic of international migration, we find that studies related to the determinants of migrations are few. Most studies on international migration came to study the relationship of migration with some economic variables without looking at the causes and motives of this migration, such as the studies on migrations to the United States of America, (Karemera et al. 2000) and (Greenwood and McDowell, 1999), and the study of international migration to the United Kingdom (Mitchell and Pain, 2003), and the migration to Germany, (Voglar and Rotte, 2000); (Fromentin, 2013) study was on the relationship between international migration and unemployment in France. Several studies have adopted the theoretical framework in the migration model, whereby potential immigrants choose the country that presents the benefits they seek, and thus the immigration decision is a function of the push and pull factors according to the following: (Grogger and Hanson, 2011), (Ortega and Peri, 2013). Where and the destination country (f). is the cost of migration. Assume that The cost of migration can be illustrated as follows: Where includes all direct and indirect costs, while means the non-monetary costs that relate to the immigrant himself, such as moving away from family and friends. (Borjas, 1987) assumes that an individual's wages depend on his skill level si, and thus the wages of the individual in either the country of origin or the host country are as follows: As long as the individual is looking to maximize his benefit, he will choose migration if is greater than zero. Thus, we can include a set of variables related to the push and pull factors in equation ( 4), so the study can examine the effect of these factors on the individual's decision to migrate. Numerous literatures on international migration has relied on random utility maximization models by combining various factors into the gravity model, which has become common in statistical analysis, especially with regard to measuring bilateral flows between two geographical regions. This model was based mainly on the law of gravity between objects developed by the "Newton" and named (Newton's law) in 1687, which states that the attraction forces between two bodies are directly proportional to their size and inversely proportional to the distance between them. This model is no longer confined to the science of physics but has become used in many sciences, especially the study of economic phenomena, related to the movement of goods, services, capital and individuals. The spatial interaction has been likened to the law of gravity. One of Volume XX Issue VI Version I c - ) ih + t ih (w - ) if + t if = (w ihf m if w and w ih refer to the wage of the individual (i) in the origin country (h), t if and indicates the benefits granted to the individual. ih t ihf c ) < 0 ih w , if t ( cov ) <0 , if w , if t ( cov , )>0 ih w , if w ( cov ihf z ) + hf x ( hf c = ihf c (1) (2) hf x ihf z I s h ? + h ? = ih W I , s f ? + f ? = if W (3) By subtracting equations ( 3), ( 2), (1) we produce the following equation: ihf z - ) hf x ( hf c - ) ih t - i f t ) + ( h ? - f ? ) + ( h ? - f ? = ( ifh m (4) ) ifh m ( the first researchers who used this model is (Tinbergen, 1962). The basic form is as follows: (Burger et al. 2009) Where: g is the Constant of the equation m i is the size of the sending country m j is the size of the receiving country d ij is the distance between the two countries GF ij is the power generated by gravity between the two countries As this model became dominant in applied studies in the field of international migration, it was enhanced to include variables that indicate factors of push and pull to understand the determinants of migration. IV. # Econometric Model Even though studies differ in determining the factors of gravity explained by the phenomenon of migration flow between countries according to the nature of the study and the views of researchers, but never the less they shared the use of basic variables in the traditional model such as: the population of sending countries and receiving countries and the distance between countries. For the purpose of the study we added other variables to the gravity model; as many studies that were conducted to explain the factors affecting international migration and its determinants supported the addition of demographic, economic, political and social variables; Thus, the form of the regression equation to study the determinants of international migration will be as follows: The dependent variable is immig ij , which expresses the number of migrants between the sending and receiving countries, while the other variables act as independent variables, and the symbols in the form indicate: i is the sending country, j is the receiving country, t denotes time, e to the error term, pop is the number of population in each country, dis is the distance between the two countries, gdpcap is per capita income in each country, ur is an unemployment rate, edu is the average years of education, gini is the inequality index of income distribution, polscor, is the political stability index, pov is the poverty index, dcomlang is an dummy variable equal to one if the two countries speak the same language, Emig is the stock of immigrants from the sending country in the receiving country, and c 0 to c 13 denote the parameters to be estimated. The unbalance panel data were used, which is distinguished in that it combines the cross-section data and time series data, which contributes to increasing degrees of freedom, which in turn increases the efficiency of the estimate and raises the explanatory power of the regression (Gujarati, 2003). V. # Estimation Strategy To avoid the problems facing estimating the gravity model in commercial exchange and spatial mobility, by giving the dependent variable the logarithmic form, the search for an alternative and more appropriate estimation technique for the gravity model has become necessary. a number of researchers directed attention to the quality of using the count data estimator in estimating the gravity model. (Silva and Teneyro, 2006) (Wooldridge, 2012). # a) Poisson Maximum Likelihood Estimator (PML) This method of estimation is applied when the dependent variable takes a valid positive value (0,1,2,3?..). This variable may take many small values including zero, and when being estimated the dependent variable is not in the logarithmic form. the count data form follows the following equation. Equation ( 6) is a nonlinear equation where the exponential function is a nonlinear function. Greene (2002) considered that this method is the best method to accommodate the heterogeneity of cross-sectional data over time, as this estimation is characterized by equal variance with the mean of the data that follows the Poisson distribution, since this distribution is assumed to have a conditional mean, in the sense that the dependent variable is required for the factors of push and pull factors. for the purposes of the assessment, it is written: # b) Maximum Likelhood Negative Binomial (NBM L) This method is an example of a Poisson estimator, when the dependent variable follows count data, which takes positive integer values, with repeated numbers from zero and small values, and the variance exceeds the mean of E (Y)