In the United States, higher education is an optional stage of formal learning following secondary education. It is also referred as post-secondary education, third-stage, third-level, or tertiary education. It covers stages 5 to 8 on the International ISCED 2011 scale. It is delivered at 4,360 Title IV degree-granting institutions, known as colleges or universities. These may be public or private universities, research universities, liberal arts colleges, community colleges, or for-profit colleges. US higher education is loosely regulated by the government and by several third-party organizations. In Spring 2022, about 16 million students—9.6 million women and 6.6 million men—enrolled in degree-granting colleges and universities in the U.S. Of the enrolled students, 45.8% enrolled in a four-year public institution, 27.8% in a four-year private institution, and 26.4% in a two-year public institution. College enrollment has declined every year since a peak in 2010–2011 and is projected to continue declining or be stagnant for the next two decades. Strong research funding helped elite American universities dominate global rankings in the early 21st century, making them attractive to international students, professors and researchers. Other countries, though, are offering incentives to compete for researchers as funding is threatened in the US and US dominance of international tables has lessened. The system has also been blighted by fly-by-night schools, diploma mills, visa mills, and predatory for-profit colleges. There have been some attempts to reform the system through federal policy such as gainful employment regulations, but they have been met by resistance. According to Pew Research Center and Gallup poll surveys, public opinion about colleges has been declining, especially among Republicans and the white working class. The higher education industry has been criticized for being unnecessarily expensive, providing a difficult-to-measure service which is seen as vital but in which providers are paid for inputs instead of outputs, which is beset with federal regulations that drive up costs, and payments coming from third parties, not users. In a 2018 Pew survey, 61 percent of those polled said that US higher education was headed in the wrong direction. A 2019 Gallup survey found that, among graduates who strongly felt a purpose in life was important, "only 40 percent said they had found a meaningful career after college." In 2020, when the COVID-19 pandemic upended regular campus life forcing students to take online classes at home, more than 100 colleges, both public and private have been sued for tuition refunds,