Heckman's lectures established a general framework for the study of inequality. First, he noted that it is difficult to define the optimal level of inequality, because inequality can arise as a market signal (as in "good" inequality where skills are rewarded in the market), whereas there also can be inequality due to discrimination and denial of opportunity. Next, he explored recent trends and statistics on inequality in the OECD and developing countries, as well as contributing factors such as household structure changes, assortative mating, and changes in the distribution of wages and returns to education. He also discussed the relationship between income and consumption inequality, the relationship between income or perceived relative position and health, and intra-family processes that contribute to population-level trends in intergenerational mobility.