graduate school, but that pattern is less common in the sciences and humanities than in engineering, education, and other professional areas.
Once enrolled, the median time actually registered in graduate study ("registered time-to-degree") for 1994 graduates ranged from 6.7 years in the physical sciences to 8.5 years in the humanities (see Figure 2-2). This measure is not the same as years enrolled in a doctoral program, since students may enroll first in a master's or other post-baccalaureate program or may take time out for employment once enrolled. Although a longer time-to-degree (registered or not) does not necessarily lead to noncompletion for any individual student, the likelihood of not completing the degree increases with each additional year in doctoral study, based simply on the fact that each additional year of doctoral study carries with it a positive chance that a student will decide to drop out.
Attrition from graduate study refers to a reduction in the number of individuals pursuing the Ph.D. The most accurate calculation of "attrition" depends on the specification of a group or cohort of students who begin doctoral study at the same time and then a later look at that cohort to determine the proportion of students having completed their degrees by a certain time (to derive a "completion rate") or the proportion of