Cohort Selection

We divide the students into cohorts based on the quarter they were admitted. This ensures that the students in each cohort will have comparable "histories" of quarterly activities, which are the focus of this study. The vast majority of the students were admitted in fall quarters, so sometimes we will refer to a fall quarter cohort by its year, e.g. the Fall 2006 Cohort would simply be the 2006 Cohort.

In each cohort, we further exclude the following students:

• Students with 45 or more transferred units. Our study is focused on First-Time Freshmen (FTF) students. Students with significant amount of transferred units are effectively transfer students even though they may be categorized as FTF in the original data.
• Students didn't enroll in the quarter they were admitted. Most of these students never enrolled at all, so it's meaningless to talk about them dropping out. The rest of the students in this group eventually enrolled in a later quarter, in which case they are better considered in the cohort of that quarter.