Economic inequality
Measurements

In 1820, the ratio between the income of the top and bottom 20 percent of the world's population was three to one. By 1991, it was eighty-six to one. A 2011 study titled "Divided we Stand: Why Inequality Keeps Rising" by the Organisation for Economic Co-operation and Development (OECD) sought to explain the causes for this rising inequality by investigating economic inequality in OECD countries; it concluded that the following factors played a role:

The study made the following conclusions about the level of economic inequality:

A 2011 OECD study investigated economic inequality in Argentina, Brazil, China, India, Indonesia, Russia, and South Africa. It concluded that key sources of inequality in these countries include "a large, persistent informal sector, widespread regional divides (e.g., urban-rural), gaps in access to education, and barriers to employment and career progression for women."

A study by the World Institute for Development Economics Research at United Nations University reported that the richest 1% of adults alone owned 40% of global assets in the year 2000. The three richest people in the world possess more financial assets than the lowest 48 nations combined. The combined wealth of the "10 million dollar millionaires" grew to nearly $41 trillion in 2008.

Oxfam 's 2021 report on global inequality said that the COVID-19 pandemic has increased economic inequality substantially; the wealthiest people across the globe were impacted the least by the pandemic and their fortunes recovered quickest, with billionaires seeing their wealth increase by $3.9 trillion, while at the same time the number of people living on less than $5.50 a day likely increased by 500 million. According to economist Joseph Stiglitz, the pandemic's "most significant outcome" will be rising economic inequality in the United States and between the developed and developing world. The 2024 Oxfam report found a significant increase in inequality as roughly five billion people have become poorer while at the same time the fortunes of the five richest individuals have doubled. The report warns that current trends are paving the way for the world's first trillionaire within a decade and global poverty eradication being postponed for 229 years.

According to PolitiFact, the top 400 richest Americans "have more wealth than half of all Americans combined." According to The New York Times on July 22, 2014, the "richest 1 percent in the United States now own more wealth than the bottom 90 percent". Inherited wealth may help explain why many Americans who have become rich may have had a "substantial head start". A 2017 report by the IPS said that three individuals, Jeff Bezos, Bill Gates and Warren Buffett, own as much wealth as the bottom half of the population, or 160 million people, and that the growing disparity between the wealthy and the poor has created a "moral crisis", noting that "we have not witnessed such extreme levels of concentrated wealth and power since the first gilded age a century ago." In 2016, the world's billionaires increased their combined global wealth to a record $6 trillion. In 2017, they increased their collective wealth to 8.9 trillion. In 2018, U.S. income inequality reached the highest level ever recorded by the Census Bureau.

The existing data and estimates suggest a large increase in international (and more generally inter-macroregional) components between 1820 and 1960. It might have slightly decreased since that time at the expense of increasing inequality within countries. The United Nations Development Programme in 2014 asserted that greater investments in social security, jobs, and laws that protect vulnerable populations are necessary to prevent widening income inequality.

There is a significant difference in the measured wealth distribution and the public's understanding of wealth distribution. Michael Norton of the Harvard Business School and Dan Ariely of the Department of Psychology at Duke University found this to be true in their research conducted in 2011. The actual wealth going to the top quintile in 2011 was around 84%, whereas the average amount of wealth that the general public estimated to go to the top quintile was around 58%.

According to a 2020 study, global earnings inequality has decreased substantially since 1970. During the 2000s and 2010s, the share of earnings by the world's poorest half doubled. Two researchers claim that global income inequality is decreasing due to strong economic growth in developing countries. According to a January 2020 report by the United Nations Department of Economic and Social Affairs, economic inequality between states had declined, but intrastate inequality has increased for 70% of the world population over the period 1990–2015. In 2015, the OECD reported in 2015 that income inequality is higher than it has ever been within OECD member nations and is at increased levels in many emerging economies. According to a June 2015 report by the International Monetary Fund (IMF):

Widening income inequality is the defining challenge of our time. In advanced economies, the gap between the rich and poor is at its highest level in decades. Inequality trends have been more mixed in emerging markets and developing countries (EMDCs), with some countries experiencing declining inequality, but pervasive inequities in access to education, health care, and finance remain.

In October 2017, the IMF warned that inequality within nations, in spite of global inequality falling in recent decades, has risen so sharply that it threatens economic growth and could result in further political polarization. The Fund's Fiscal Monitor report said that "progressive taxation and transfers are key components of efficient fiscal redistribution." In October 2018 Oxfam published a Reducing Inequality Index which measured social spending, tax and workers' rights to show which countries were best at closing the gap between the rich and the poor.

The 2022 World Inequality Report, a four-year research project organized by the economists Lucas Chancel, Thomas Piketty, Emmanuel Saez, and Gabriel Zucman, shows that "the world is marked by a very high level of income inequality and an extreme level of wealth inequality" and that these inequalities "seem to be about as great today as they were at the peak of western imperialism in the early 20th century." According to the report, the bottom half of the population owns 2% of global wealth, while the top 10% owns 76% of it. The top 1% owns 38%.
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