Introduction

Economic inequality is widespread and to some extent inevitable. It is our belief, however, that where rising inequality is not properly addressed, it leads to all manner of political and social catastrophes. Avoiding these begins with careful monitoring.

In all societies, human beings care deeply about inequality. Changes in inequality levels have concrete consequences for people’s living conditions, and they challenge our most basic and cherished notions of justice and fairness. Are different social groups getting all they deserve? Is the economic system treating different categories of labor-income earners and property owners in a balanced and equitable manner, both locally and globally? Across the world, people hold strong and often contradictory views on what constitutes acceptable and unacceptable inequality.

Again, to some extent, this will always be so. Our objective is not to bring everyone into agreement about inequality: this will never happen, for the simple reason that no single, scientific truth exists regarding the ideal level of inequality, let alone the ideal social policies and institutions to achieve and maintain it. Ultimately, it is up to public deliberation and political institutions and processes to make these difficult decisions.

Still, without aspiring to make everyone agree on the ideal level of inequality, we can hope and believe it is possible to agree about a number of inequality facts. The immediate objective of this report is to bring together new data series from the World Wealth and Income Database (WID.world) to document a number of newly discovered trends in global inequality.

WID.world is a cumulative and collaborative research process that originated in the early 2000s, and now includes over one hundred researchers covering more than seventy countries on all continents. WID.world provides open access to the most extensive available database on the historical evolution of the world distribution of income and wealth, both within and between countries.

In the context of the present report, we are able to present novel findings along three major lines. First, thanks to newly available data sources, we provide better coverage of emerging countries and of the world as a whole. Until recently, studies of inequality have tended to focus on the developed countries of Europe, North America, and Japan, largely due to better data access. Beginning with the World Inequality Report 2018 we are able to present findings on inequality dynamics in emerging and developing countries, including China, India, Brazil, South Africa, Russia, and the Middle East. We show that inequality has increased in most world regions in recent decades, but at different speeds, suggesting that different policies and institutions can make a substantial difference. Such geographic coverage now allows us to track income growth rates of global income groups and analyze inequality among world citizens.

Second, we cover the entire distribution of incomes, from the bottom to the top, in a consistent manner. Until recently, most available long-run series on inequality focused on top-income shares. In this report, we present new findings on how the shares going to the lowest groups of populations have evolved. We show that bottom-income shares have declined significantly in many countries. In particular, we document a dramatic collapse of the bottom 50% income share in the United States since 1980 but not in other advanced economies, again suggesting that policies play a key role.

Third, our new series allow us to analyze the distribution of wealth and the structure of property in terms of how these have evolved. Most available series on inequality have focused on income rather than wealth. We are able in the World Inequality Report 2018 to present new findings on the changing structure of public versus private wealth and the concentration of personal wealth. We show that net public wealth (assets minus debt) is close to zero or even negative in many developed countries, which stands in contrast to the situation observed in some emerging countries (most notably China).

These are important analytical advances, yet we are very much aware that we still face heavy limitations in our ability to measure the evolution of income and wealth inequality. Our objective in WID.world and in the World Inequality Report is not to claim that we have perfect data series, but rather to make explicit what we know and what we do not know. We attempt to combine and reconcile in a systematic manner the different data sources at our disposal: national income and wealth accounts; household income and wealth surveys; fiscal data coming from taxes on income, inheritance, and wealth (when they exist); and wealth rankings.

None of these data sources and their associated methodologies is sufficient in itself. In particular, we stress that our ability to measure the distribution of wealth is limited, and that the different data sources at our disposal are not always fully consistent with one another. But we believe that by combining these data sources in ways that are reasonable and explicitly described we can contribute to a better informed public debate. The methods and assumptions underlying our series are transparently presented in research papers available online. We make all raw data sources and computer codes easily accessible so that our work can be reproduced and extended by others.

Part of our aim is to put pressure on governments and international organizations to release more raw data on income and wealth. In our view, the lack of transparency regarding inequality of income and wealth seriously undermines the possibilities for peaceful democratic discussion in today’s globalized economy. In particular, it is critical that governments provide public access to reliable and detailed tax statistics, which in turn requires that they operate properly functioning reporting systems for income, inheritance, and wealth. Short of this, it is very difficult to have an informed debate about the evolution of inequality and what should be done about it.

Our most important reason for providing all the necessary details about data sources and concepts is to enable interested citizens to make up their own minds about these important and difficult issues. Economic issues do not belong to economists, statisticians, government officials, or business leaders. They belong to everyone, and it is our chief objective to contribute to the power of the many.