the G.I. Bill. Because Vassar's charter prohibited male matriculants, the graduates were given diplomas via the University of the State of New York. These were reissued under the Vassar title after the school formally became co-educational. The formal decision to become co-ed came after its trustees declined an offer to merge with Yale University, its sibling institution, in the wave of mergers between the historically all-male colleges of the Ivy League and their Seven Sisters counterparts. In its early years, Vassar was associated with the social elite of the Protestant establishment. E. Digby Baltzell writes that "upper-class WASP families educated their children at colleges such as Harvard, Princeton, Yale, and Vassar." A select and elite few of Vassar's students were allowed entry into the school's secret society Delta Sigma Rho, started in 1922. Before becoming President of the United States, Franklin Delano Roosevelt was a Trustee. Roughly 2,450 students attend Vassar, and 98% live on campus. About 60% come from public high schools, and 40% come from private schools (both independent and religious). Vassar is currently 56% women and 44% men, at national average for national liberal arts colleges. Students are taught by more than 336 faculty members, virtually all holding the doctorate degree or its equivalent. The student-faculty ratio is 8:1, average class size, 17. In recent freshman classes, students of color constituted 32–38% of matriculants. International students from over 60 countries make up 8-10% of the student body. In May 2007, in keeping with its commitment to diverse and equitable education, Vassar returned to a need-blind admissions policy wherein students are admitted by their academic and personal qualities, without regard to financial status. Vassar president Frances D. Fergusson served for two decades. She retired in the spring of 2006, and was succeeded by Catharine Bond Hill, former provost at Williams College, who served for 10 years until she departed in 2016. Hill was replaced by Elizabeth Howe Bradley in 2017. The college was listed as a census-designated place (Vassar College CDP) in 2019. Presidents Campus Architecture Vassar's campus, also an arboretum, is and has more than 100 buildings, ranging in style from Collegiate Gothic to International, with several buildings of architectural interest. At the center of campus stands Main Building, one of the best examples of Second Empire architecture in the United States. When it was opened, Main Building was the largest building in the U.S. in terms