Does Education Pay in Urban China? Estimating Returns to Education Using Twins

This paper empirically estimates the returns to education using twins data that the authors collected from urban China. Our ordinary least-squares estimate shows that one year of schooling increases an individual¡¦s earnings by 8.4 percent. However, once we use the within-twin-pair fixed effects model, the return is reduced to 2.7 percent, which suggests that much of the estimated returns to education in China that have been found in previous studies are due to omitted ability or the family effect. This finding suggests that well-educated people are faring well in China mainly because of their superior ability or family background advantages, rather than because of knowledge that they acquired at school. We further investigate why the true return is low and the omitted ability bias high, and find evidence that it may be a consequence of the distinct education system in China, which is highly selective and exam oriented. More specifically, we find that high school education mainly serves as a mechanism to select college students, and has zero returns in terms of earnings. In contrast, both vocational school education and college education have a large return that is comparable to that found in rich Western countries.

Economic Returns to Communist Party Membership: Evidence from Chinese Twins

This paper empirically estimates the returns to membership of the Chinese Communist Party using unique twins data that the authors collected from urban China. Our ordinary least squares estimate shows that being a Party member increases earnings by 28.1 percent, but when we use a within-twin-pair fixed-effects model, the effect of Party membership all but disappears, which suggests that much of the estimated value of Party membership that is given in the literature is due to the effects of omitted ability or family background. The findings suggest that Party members fare well not because of their special political status per se, but because of the superior ability that allowed them to pass through the strict Party membership selection process.

Dynamic simulation analysis of spur gear space driven system with large inertia load

The wide application of large inertia loads in space drive mechanisms is relatively rare in theoretical research. An 8-degree-of-freedom nonlinear dynamic model is established for the time-varying and nonlinear perturbation problems of a large inertia load space drive mechanism. The model is a two-stage spur gear model in which the effects of backlash and time-varying stiffness are considered. The 3D model was imported into ADAMS, and the nonlinear dynamic response of the system was studied by motion simulation. This paper sets up a large inertia experimental device to collect and process data. Comparing experimental results with Adams results, the correctness of the numerical model was verified, and the reasons for the differences between the two were explained. A comparative analysis of the load response under different inertia was performed to illustrate the importance of studying large inertia loads. The simulation results show that the output shaft has a great influence on the dynamic response. Changing the material of the gear can improve the transmission precision of the gear system. The analysis results in this paper enrich the research on the dynamic response of gear system, and provide a theoretical basis for the subsequent design of large inertia load gear system and improve vibration and noise during operation