from the new Forbes list (where Northeastern does terribly) methodology page:
http://www.forbes.com/sites/carolinehoward/2015/07/29/ranking-americas-top-colleges-2015/2/
Graduation Rate (7.5%)
There are many valid reasons why students take an additional year (or two) to graduate. Universities such as Northeastern require time spent on “co-ops,” or extracurricular learning. Individual students may take time off to for work, service or travel. Our concern, though, is a strict four-year graduation rate, which can save students and their families tens of thousands. CCAP evaluates how many students actually finish their degrees in four years, considering both the actual graduation rate (5%) and the actual vs. predicted rate (2.5%).