Partner choice and parameter estimates: modelling the effect of preferences

Agent-based simulations of marriage processes are used to investigate whetherloglinear models of tables of spouse pairs properly capture evidence of the preferences behind assortative mating. Can we tell what sort of mechanisms bring about the patterns we see? Is there a female hypergamy preference and do loglinear models capture it? Four different ideal-typical simulations of spouse choice processes are presented: homophily, competition, social segregation, time segregation. All produce "realistic" patterns of educational assortative mating. Imposing a simulated female hypergamy preference yields more asymmetric outcomes, directly detected in loglinear models. But the relationship between the size of the hypergamy estimate and the strength of the hypergamy differs according to the pairing mechanism. Notably, for homophily the estimate is lower, and for time-segregation higher. Indeed, for zero simulated hypergamy, the homophily simulation shows negative, and the time-segregation simulation positive, hypergamy. This is shown to be due to the dynamic nature of the simulations: as individuals pair off the distribution of single individuals changes. For homophily perfectly symmetric choices at each iteration sum into a table of spouse pairs in which loglinear models detect hypogamy. Conclusions: these biases are small, and depend on very large simulation populations. They are less likely to be detectable in typical survey data. However, we demonstrate a clear mechanism by which loglinear models of tables of spouse pairs can be biased. This suggests that if longitudinal data is available, a time dimension should be included in the loglinear models. Otherwise, this is another argument for preferring tables of recent marriages.

Segregation simulation of binary granular matter under horizontal pendulum vibrations

Segregation of binary granular matter with different densities under horizontal pendulum vibrations was investigated through numerical simulation using a 3D discrete element method (DEM). The particle segregation mechanism was theoretically analyzed using gap filling, momentum and kinetic energy. The effect of vibrator geometry on granular segregation was determined using the Lacey mixing index. This study shows that dynamic changes in particle gaps under periodic horizontal pendulum vibrations create a premise for particle segregation. The momentum of heavy particles is higher than that of light particles, which causes heavy particles to sink and light particles to float. With the same horizontal vibration parameters, segregation efficiency and stability, which are affected by the vibrator with a cylindrical convex geometry, are superior to that of the original vibrator and the vibrator with a cross-bar structure. Moreover, vibrator geometry influences the segregation speed of granular matter. Simulation results of granular segregation by using the DEM are consistent with the final experimental results, thereby confirming the accuracy of the simulation results and the reliability of the analysis.