Durlauf 's subsequent lecture included a rigorous discussion of the calculation and theoretical formulation of intergenerational mobility, which is a key concept for tracking trends in inequality and projection of future inequality. He reviewed developments in the calculation of intergenerational elasticity of income including the importance of isolating permanent income rather than transitory shocks, cross-country comparisons, identification of poverty traps, and the application of Markov models and social interaction models. In addition to intergenerational persistence of income, Durlauf explored intergenerational persistence in characteristics such as crime, fertility, and cigarette smoking. He presented models of the determinants of intergenerational persistence including neighborhoods, social interactions, and assortative mating; multi-dimensional skill development and family investment; and the roles of credit constraints and genetics.