## 5 Discussion and Conclusion  
This study combines the employment multiplier theory with the theory of urban development stage and selects cities in the process of growth as the research unit to estimate the employment multiplier. It not only has significance for policymaking, but also improves the employment multiplier theory. The change in non-tradable sector employment caused by manufacturing growth in each city is calculated by using the sub-industry data of Chinese prefectural cities, and the difference in this multiplier among different cities is explained by taking city size and trade sector specialization degree as the main explanatory variables. It is of great practical significance to confirm and estimate the differences in employment multipliers between cities. Local differences should be considered in the relevant policies formulated by local governments to promote employment. The multipliers in terms of countries or large regions affirm the importance of changes in the trade sector to regional development, but these are insufficient to answer the question of how to increase the employment multiplier in a city. This study weakened the error range by distinguishing expanding cities from cities which had different multipliers when expanding or shrinking. The multipliers would be underrated if all cities were put into one model. According to the calculations in this study, the average multiplier of Chinese cities is 1.67, which is close to the previous research results [22]. However, a slightly higher value, not surprisingly, suggests the importance of dividing cities into expanding and shrinking cities. The situation by region and scale is consistent with the research conclusions of other scholars [17; 23; 32]. It also proves the robustness of the sub-city calculation. Furthermore, it confirms the employment multiplier in the expansion and contraction of the difference between the process and the expansion of the larger number. In the study of urban problems, urban size once again played an important role. Regression results confirmed the size of the cities in the process of employment change. This is because of the expansion of the city scale and the change in the types of consumer-market scales. The consumption expenditure of urban residents increases with the expansion of the local consumption market. Furthermore, the more significant multilevel employment promotion effect was brought about by the job increase in the trade sector. City size is important not only in the general sense, but also in different regions. It can be seen from the regression results that the coefficient of urban size in the western region is larger than that in other regions, indicating that the efficiency advantage of large cities should be brought into play in the western region with sparse population; this is also revealed laterally, so small cities have greater difficulty in realizing the same multiplier effects. The specialization of the tradable sector is the guarantee of employment multipliers and even urban development. This is reflected in employment level, and urban residents' incomes have far-reaching influences on the speed and sustainability of urban development; this is consistent with [PERSON]'s conclusion [41]. Therefore, the ability to produce tradable products professionally warrants close attention. China differs from developed countries regarding the impact of factors such as labor costs and housing costs on the employment multiplier. In [PERSON]'s explanation of the multiplier, factors such as labor cost and housing cost have a correction and adjustment effect on the employment multiplier [11; 14]. The results show that these factors are not significant in China, which is also one of the differences between developing countries and developed countries. The low level of urbanization in developing countries means that many agricultural workers can enter the labor pool in cities, thus improving the elasticity of the urban labor supply.