A 2011 study psychologists Shigehiro Oishi, Ulrich Schimmack, and Ed Diener, using data from 54 countries, found that progressive taxation was positively associated with the subjective well-being, while overall tax rates and government spending were not. The authors added, "We found that the association between more-progressive taxation and higher levels of subjective well-being was mediated by citizens’ satisfaction with public goods, such as education and public transportation."[1] Tax law professor Thomas D. Griffith, summarizing research on human happiness, has argued that because inequality in a society significantly reduces happiness, a progressive tax structure which redistributes income would increase welfare and happiness in a society.[44] Since progressive taxation reduces the income of high earners and is often used as a method to fund government social programs for low income earners, calls for increasing tax progressivity have sometimes been labeled as envy or class warfare,[3][45][46] while others may describe such actions as fair or a form of social justice.[46][47]