as opposed to ungrouped dormitories or "residential colleges" as employed at such institutions as yale university or princeton university (in imitation of the colleges of cambridge and oxford), dartmouth residence halls are grouped into nine "communities," each composed of one to three "clusters" of dormitories. dartmouth houses approximately 3,300 students in its facilities, or about 85% of the student body; the remaining 15% opt to live in off-campus housing. the housing office consists of three employees that house students four times a year (not including the interim period), due to the college's enrollment plan (the "d-plan").