Ph.D. completion data table follows 3 entering cohorts of students and summarizes the number of students who completed the Ph.D. degree, the number of students who left without any degree, the number of students who left with a Master’s degree, and the number of students who successfully passed Ph.D. comprehensive (“comp”) exams. Data are also provided on number of students and the approximate time (<6 - >8 years) required to complete the degree, the number of students still enrolled, and the 8-year completion percentage—that is, of the students who entered the degree program originally for a given year, the percentage who completed the Ph.D. within 8 years.
Keep in mind that there may be many reasons for students to not complete a Ph.D. program; e.g., some move to other institutions, some change majors, some have personal circumstances that intervene, and some complete with a master’s degree. You can find the completion data for programs across the U.S. (for 2005-06) by visiting the National Research Council Assessment of Research Doctoral: https://www.nationalacademies.org/our-work/an-assessment-of-research-doctorate-programs