Higher education in the United States is an optional stage of formal learning following secondary education. Higher education, also referred to as post-secondary education, third-stage, third-level, or tertiary education occurs most commonly at one of the 4,360 Title IV degree-granting institutions, either colleges or universities in the country. These may be public universities, private universities, liberal arts colleges, community colleges, or for-profit colleges. US higher education is loosely regulated by several third-party organizations. Within this vast estate many issues arise for government, staff and students. Political views Research since the 1970s has consistently found that professors are more liberal and Democratic than the general population. A 2007 Zogby poll found that 58% of Americans thought that college professors' political bias was a "serious problem". This varied depending on the political views of those asked. 91% of "very conservative" adults agreed compared with 3% of liberals. A nationwide study conducted every three years by the Higher Education Research Institute (HERI) of UCLA shows that from 1989 to 2014 professors identifying as liberal or far-left increasingly outnumbered those identifying as conservative or far-right. The shift from 2014 to 2017 was less extreme than prior years, with numbers standing at approximately 60% liberal/far-left, 28% moderate, and 12% conservative/far-right. According to an article published in Academe, the impact of having more liberal professors meant that fewer conservative students were likely to pursue advanced or doctoral degrees. According to Stephen Hayward, the fewer conservative professors results in fewer conservative students being mentored and supported to seek graduate level education, creating a "self-reinforcing" cycle. In 2012, Tilburg University psychologists Yoel Inbar and Joris Lammers conducted anonymous random surveys of 800 members of the Society for Personality and Social Psychology and found that 85% of respondents self-identified as liberal and 6% self-identified as conservative. Respondents that self-identified as either conservative or moderate were found to be significantly more reluctant to express their political views to their colleagues for fear of negative consequences, and were more likely to believe that their colleagues would actively discriminate against them on the basis of their political beliefs. In January 2015, a major literature review co-written by psychologists José L. Duarte, Jarret T. Crawford, Jonathan Haidt, Lee Jussim, Philip E. Tetlock and sociologist Charlotta Stern summarized numerous studies of how academic psychology has little ideological diversity, that the ratio of liberal-to-conservative or Democratic-to-Republican professors has dramatically increased since 1990, that the disparity