Galor–Zeira model
The Galor-Zeira model is the first macroeconomic model to explore the role of heterogeneity in the determination of macroeconomic behavior. In contrast to the representative agent approach that dominated the field of macroeconomics till the early 1990s and argued that heterogeneity has no impact on macroeconomic activity, the model demonstrates that in the presence of capital markets imperfections and local non-convexities in the production of human capital, income distribution affects the long run level of income per-capita as well as the growth process.   The model was developed by Oded Galor and Joseph Zeira in  1988, and it was published in the paper “Income Distribution and Macroeconomics”, 1993. Thesis. In contrast to the Neoclassical paradigm and the representative agent approach that denied the role of inequality in the growth process, novel theories that emerged in the late 1980s and empirical studies of these theories have established that income distribution has a significant impact on the process of development. The modern perspective, originated by Galor and Zeira (1988, 1993), has underscored the role of heterogeneity in the determination of macroeconomic activity, and has demonstrated that income distribution is an important determinants of the growth process and  the evolution of income per capita. In particular, Galor and Zeira have argued that since credit markets are imperfect, inequality has an enduring impact on human capital formation, the level of income per capita, and the growth process. In contrast to the classical paradigm, which underlined the positive implications of inequality for capital formation and economic growth, Galor and Zeira’s hypothesis suggests that inequality has an adverse effect on human capital formation and economic development, in all but the very poor economies. The Galor-Zeira model suggests that the impact of inequality on the growth process, is governed by  the effect of unequal access to education, due to imperfect capital markets, on human capital formation and economic growth. The initial distribution of income determines whether an economy converges to a low-education, low-income steady-state equilibrium, or high-income, high education steady-state equilibrium. In particular, the model predicts that inequality have an adverse effect on human capital formation and economic growth in all but the very poor economies. Testable Predictions. The Galor and Zeira’s model predicts that the effect of rising inequality on GDP per capita is negative in relatively rich countries but positive in poor  countries. These testable predictions have been examined and confirmed empirically in recent studies. In particular, Brückner and Lederman test the prediction of the model by in the panel of countries during the period 1970-2010, by considering the impact of the interaction between the level of income inequality and the initial level of GDP per capita. In line with the predictions of the model, they find that at the 25th percentile of initial income in the world sample, a 1 percentage point increase in the Gini coefficient increases income per capita by 2.3%, whereas at the 75th percentile of initial  income a 1 percentage point increase in the Gini coefficient decreases income per capita by -5.3%. Moreover, the proposed human capital mechanism that mediate the effect of inequality on growth in the Galor-Zeira model is also confirmed. Increases in income inequality increase human capital in poor countries but reduce it in high and middle-income countries. This recent support for the predictions of the Galor-Zeira model is in line with earlier and recent findings. Roberto Perotti showed that in accordance with the credit market imperfection approach, developed by Galor and Zeira, inequality is associated with lower level of  human capital formation (education, experience, apprenticeship) and higher level of fertility, while lower level of human capital is associated with lower levels of economic growth. Roland Benabou's finds that the growth process of Korea and the Philippines "are broadly consistent with the credit-constrained human-capital accumulation hypothesis." In addition, a recent study by Andrew Berg and Jonathan Ostry suggests that  inequality seems to affect growth through human capital accumulation and fertility channels.   Model & Implications. Short-run Implications. Decision to invest in education depends on parent wealth due to credit market imperfections. Long-run Implications. The society is segmented  into two dynasties (due to the fixed cost of education): Inequality affects development: Policy implications. Government policy can improve the long-run equilibrium (in non-poor economy) by: Significance. The Review of Economic Studies named the Galor-Zeira paper ("Income Distribution and Macroeconomics") among the 11 most path-breaking papers published in The Review of Economic Studies in the past 60 years.