شکاف مهاجرت و دستمزدی و بیکاری بین بخش های شهری و غیرشهری: تفسیر مجدد تعادل عمومی پویا از تعادل هریس تودارو

his paper offers a dynamic general equilibrium reinterpretation of the static partial migration equilibrium by Harris and Todaro [Harris, J., Todaro, M., 1970. Migration, unemployment and development; a two-sector analysis. American Economic Review 60, 126–142], under (i) flexible urban and rural wages and (ii) free mobility of workers and free entry of firms. The proposed model accounts for the set of stylized facts in developing countries: rural to urban migration and higher urban wages and unemployment. The model allows us to view the wage gap as a compensating differential for the negative amenities associated with job destruction and subsequent costly search on the consumption side, which can also be seen as a match-specific premium based on a sectoral productivity differential on the production side. Our model predicts the comovements among urban and non-urban wages and migration flows to the urban sector, an empirical regularity observed over the urbanization process of developing economies. Finally, we also conduct a welfare analysis.

Three salient stylized facts that characterize the economic development process are: (i) workers migrate from the rural to the urban sector, (ii) wages in the urban sector exceed those in the rural sector, and (iii) urban unemployment exceeds that in the rural sector.1 While these phenomena are common across developing economies, it has been difficult to obtain a cogent theoretical explanation. The early seminal papers by Harris and Todaro (1970) (henceforth, HT) and Todaro (1969) took some important strides toward providing an explanation. In its simplest form, HT's model postulates that migration proceeds in response to differences in urban and rural “expected” wages, and the HT equilibrium holds when the expected wages are equalized.2 Nevertheless, a caveat to their approach is that migration is considered in a partial equilibrium setting with urban wages given exogenously. Moreover, the equilibrium is defined based on ex ante expected value calculations. But given the differences in job-finding and -destruction rates in the usual job-matching process entailing costly and time-consuming search, such ex ante HT migration decisions are not supported by the ex post decisions in a dynamic general equilibrium setting. 3 This point therefore implies that migratory flows in the traditional HT models are not an ongoing equilibrium phenomenon. While many important studies have extended or improved the HT migration equilibrium (see the literature survey in footnote 4),4 what separates this study from previous studies lies in the following three points. First, this paper builds a dynamic general equilibrium model of migratory flows that is consistent with the set of stylized facts. The proposed model provides a coherent framework that permits: (i) both urban and rural wages to be fully flexible, (ii) both labor mobility and firm entry to be free across sectors and (iii) unmatched workers and firms to conduct costly and time-consuming search, such that it still keeps the original motivation of HT as closely as possible. In such an environment, it is possible to address questions concerning migration flows and the evolution of relative wages and relative unemployment rates as development actively takes place, not to mention a more general welfare analysis. In our model, migration occurs freely, even within a period, in response to changes in the present value of income arising from sectoral wage changes or job-finding, job-arrival, or job-destruction rates. In a general dynamic search-matching context, we can find the exact conditions for the HT equilibrium. As we will see later, for the model to explain the wage and unemployment gaps across sectors as an equilibrium phenomenon, the urban sector should exhibit the properties of (i) greater heterogeneity and specificity of jobs, and (ii) higher productivity, compared with the non-urban sector. Second, this paper presents a more structural interpretation of the wage gap. Rather than appealing to an “exogenous wage gap” between the urban and rural sectors that is large enough to compensate migrants for the risks of being unemployed (as in HT),5 the gap in this paper is endogenous and consistent with the traditional labor economics literature (e.g., Roback, 1982). It can be interpreted as a compensating differential for the negative amenities associated with job destruction and subsequent costly search in a fully general equilibrium setting on the consumption side. On the production side, it can also be seen as a match-specific premium based on a sectoral productivity differential. Given that the urban wage is exogenously set above the rural wage in the HT model, there is only one pricing instrument left that can allocate labor: the rate of urban unemployment. Thus, HT do not really tell us that a higher urban wage is a compensating differential for unemployment risk; instead, unemployment risk is a pricing scheme for scarce resources under conditions of congestion.6 Third, the proposed model predicts the comovements among urban and non-urban wages and migration flows to the urban sector, an empirical regularity observed over the urbanization process of developing economies. Along with a more structural interpretation of the wage gap, we examine the changes in rural and urban wages and migration flows over the urbanization process, which previous studies did not explore. Our view on the urban sector accords with that of Fujita and Thisse (1996), Behrman (1999), and Sato (2004): compared with non-urban jobs, urban jobs are more heterogeneous and specific. A natural implication of this point is that the urban sector faces a more costly and time-consuming job-matching process under imperfect information.7 We argue that these differences in matching technology between the sectors, when combined with a productivity differential, permit a steady-state equilibrium in which the wage gap is accounted for by a match-specific premium based on a sectoral productivity differential and the unemployment gap by urban job-search frictions (e.g., a time- and resource-consuming process). Our two-sector (urban and non-urban) job-matching model is a natural integration of the original HT model and the classic one-sector macroeconomic search-matching models of Diamond (1984) and Mortensen and Pissarides (1994). As in most matching models, unemployment occurs in the costly and time-consuming trade of labor services when workers and firms are heterogeneous and information about them is imperfect. As a result, we not only endogenize variables such as the number of displaced workers, vacancies, and job searchers, and the unemployment rate, sectoral wages, and the non-urban population, but we also allow for search externalities arising from congestion in job search and worker recruitment. The remainder of the paper consists of the following sections. Section 2 describes the basic structure of our model. Section 3 presents the steady-state equilibrium, key results, and an interpretation of them. We show that our model can account for widely observed comovement among sectoral wages and the urbanization rate. Then we conduct a welfare analysis to characterize the efficiency of the equilibrium with some new policy implications. A short summary and conclusions are given in Section 4.

Migration from the rural to the urban sector, combined with higher wages and unemployment in cities than in rural areas, has been a central issue in developing economies. We attempted to provide a dynamic general equilibrium reinterpretation of the static partial migration equilibrium by Harris and Todaro (HT) (1970), under (i) flexible urban and rural wages and (ii) free mobility of workers and free entry of firms. Our model highlights the exact conditions for the dynamic HT equilibrium to hold in a search-matching context. To explain the observed migration pattern and the wage and unemployment gaps across sectors as an equilibrium phenomenon, we showed that the urban sector should exhibit the properties of (i) greater heterogeneity and specificity of jobs and (ii) higher productivity compared with the non-urban sector. The model allows us to view the wage gap as a compensating differential for the negative amenities associated with job destruction and subsequent costly search on the consumption side, which can also be seen as a match-specific premium based on a sectoral productivity differential on the production side. The proposed model predicts the comovements among urban and non-urban wages and migration flows to the urban sector, an empirical regularity observed over the urbanization process of developing economies. Finally, welfare analysis suggests some interesting policy implications. While the sectoral productivity differential across sectors is a crucial element of our model and results, this paper did not mention what drives it and instead assumed sufficiently high urban productivity. Perhaps the differential arises from the agglomeration effect in the urban sector, given that (i) according to the new economic geography, close spatial proximity involves pecuniary externalities — it reduces the costs of trading both intermediate and final goods, and/or (ii) according to the recent economic growth literature, urban agglomeration promotes human capital accumulation through active learning. Incorporating these features into the present model seems to be a promising avenue for future research.