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Economic inequality, also known as income inequality, wealth inequality, gap between rich and poor, gulf between rich and poor and contrast between rich and poor, refers to how economic metrics are distributed among individuals in a group, among groups in a population, or among countries. Economists generally think of three metrics of economic disparity: wealth (wealth inequality), income (income inequality), and consumption.〔 The issue of economic inequality can implicate notions of equity, equality of outcome, and equality of opportunity. Some studies have emphasized inequality as a growing social problem. Too much inequality can be destructive, because income inequality and wealth concentration can hinder long term growth. Early statistical studies comparing inequality to economic growth had been inconclusive,〔 however in 2011, International Monetary Fund economists showed that greater income equality—less inequality—increased the duration of countries' economic growth spells more than free trade, low government corruption, foreign investment, or low foreign debt.〔 Economic inequality varies between societies, historical periods, economic structures and systems. The term can refer to cross sectional distribution of income or wealth at any particular period, or to the lifetime income and wealth over longer periods of time.〔Wojciech Kopczuk, Emmanuel Saez, and Jae Song find that "most of the increase in the variance of (log) annual earnings is due to increases in the variance of (log) permanent earnings with modest increases in the variance of transitory (log) earnings." Thus, in fact, the increase in earnings inequality is in lifetime income. Furthermore, they find that it remains difficult for someone to move up the earnings distribution (though they do find upward mobility for women in their lifetime). See their "Earnings Inequality and Mobility in the United States: Evidence from Social Security Data since 1937," ''Quarterly Journal of Economics''. 125, no. 1 (2010): 91–128.〕 There are various numerical indices for measuring economic inequality. A widely used one is the Gini coefficient, but there are also many other methods. ==Measurement concepts== Economists generally think of three metrics of economic disparity: wealth, income, and consumption.〔(【引用サイトリンク】url=http://www.economist.com/blogs/freeexchange/2014/07/measuring-inequality )〕 A skilled professional may have low wealth and low income as student, low wealth and high earnings in the beginning of the career, and high wealth and low earnings after the career. People's preferences determine whether they consume earnings immediately or defer consumption to the future. The distinction is also important at the level of economy: * There are economies with high income inequality and relatively low wealth inequality (such as Japan and Italy).〔 * There are economies with relatively low income inequality and high wealth inequality (such as Switzerland and Denmark).〔 There are many different ways to measure income inequality and wealth inequality. Different choices lead to different results. OECD has inspected the following 8 types of ''income inequality'' concepts: * ''Dispersion of hourly wages among full-time (or full-time equivalent) workers'' * ''Wage dispersion among workers'' – E.g. annual wages, including wages from part-time work or work during only part of the year. * ''Individual earnings inequality among all workers'' – Includes the self-employed. * ''Individual earnings inequality among the entire working-age population'' – Includes those who are inactive, e.g. students, unemployed, early pensioners, etc. * ''Household earnings inequality'' – Includes the earnings of all household members. * ''Household market income inequality'' – Includes incomes from capital, savings and private transfers. * ''Household disposable income inequality'' – Includes public cash transfers received and direct taxes paid. * ''Household adjusted disposable income inequality'' – Includes publicly provided services. There are many challenges in comparing data between economies, or in a single economy in different years. Examples of challenges include: * Data can be based on joint taxation of couples (e.g. France, Germany, Ireland, Netherlands, Portugal and Switzerland) or individual taxation (e.g. Australia, Canada, Italy, Japan, New Zealand, Spain, the UK).〔 * The tax authorities generally only collect information on income that is potentially taxable.〔 * The precise definition of gross income varies from country to country. There are differences when it comes to inclusion of pension entitlements and other savings, and benefits such as employer provided health insurance.〔 * Differences when it comes under-declaration of income and/or wealth in tax filings.〔 * A special event like an exit from business may lead to a very high income in one year, but much lower income in other years of the person's lifetime.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Economic inequality」の詳細全文を読む スポンサード リンク
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