چگونه ساختار خانواده اقتصاد شهری را شکل می دهد؟

Households in real cities are heterogeneous regarding their size and composition. This implies that the household structure – i.e. the (average) household size, the composition, the relative share of different household types, and the number of households – differs across cities. This aspect is usually completely neglected in urban models used to study economic and policy issues that arise in today's cities. Furthermore, the household structure might change over time. For instance, over the last decades average household size has decreased in many countries. Several implications of this change have been discussed, but usually not in regard to an urban economy with its interdependencies. We develop an applied urban general equilibrium model (based on Anas and Xu, 1999 or Anas and Rhee, 2006) which explicitly takes the household structure into account and thus allows studying the impacts of differences in the household structure on urban areas. The paper shows that the household structure affects an urban economy and its spatial pattern in various ways and may contribute to explain economic and spatial effects on cities and differences across cities. Compared to a ‘Base City’ which reflects the actual household structure in the United States, urban labor force participation, housing demand, rents, wages as well as urban commuting and shopping patterns are considerably affected by, e.g., differences in the average household size in a city. For instance, wage inequality between differently skilled workers raises and extreme cross commuting drops to almost zero when the city turns into a ‘Singles City’. Hence, pure economic forces associated with the household structure may shape cities in a different way, implying that the impacts of urban policies may depend on the household structure and therefore differ across cities.

The household is the fundamental basic economic unit in the society. But the structure of households varies across cities because households are heterogeneous and differ in size as well as their composition. Furthermore, the household structure – i.e. the (average) household size, the composition, the relative share of different household types, and the number of households – changes over time. For instance, in many countries households have become smaller in recent decades. Between 1970 and 2000, the average number of persons in households in less developed countries fell from 5.1 to 4.4. In more developed nations, it decreased from 3.2 to 2.5 persons per household over the same period (Keilman, 2003). Fig. 1 shows the trend in the United States.

Many countries and their cities are characterized by a prevailing trend towards smaller average household sizes. In addition, there is heterogeneity in the household structure across cities, an aspect usually completely neglected in the urban economics literature. We have addressed these issues by analyzing the impacts of differences in the household structure on an urban economy, in particular the spatial travel patterns. This is done by implementing a complex household structure into an urban general equilibrium model. Besides the usually assumed single-worker household, we have explicitly taken into account non-working single and couple households as well as homogeneous and heterogeneous two-worker households. The households differ not only in endowments and preferences, but also in size and the composition regarding their members. We found that the household structure affects an urban economy and its spatial pattern in various ways and may contribute to explain economic and spatial differences across cities as well as long term changes within cities. That is, even if cities are completely identical regarding their total number of residents as well their proportion of different skill groups, economic forces associated with the household structure may shape cities in a different way. As a consequence, the impacts of policy arrangements studied by urban economists might be influenced by the household structure and might differ across cities.