student who leaves one institution but enrolls in another institution is an institutional-
dropout but not a system-dropout. Consequently, there is no universally accepted
definition of dropout or stopout.3
In this paper, the following definition of dropout is used: a “dropout” is a student
who left college and did not return to any institution in the higher education system by
the end of the survey period (Fall 1990 in the NLSY 79 data). Under this definition, there
are two reasons for exit from college: graduation or dropout. The graduation group is
defined as those who graduated with a 4-year college degree. Some of them may have
experienced stopout periods during their college career.
3. A Competing Risks Model with Endogenous Waiting time
We consider the case where an individual experiences two distinct durations. The
first duration is the delay time between high school graduation and college enrollment.
The second duration is the duration of college attendance, which may depend on the delay
time between high school graduation and enrollment. Since educational duration data in the
NLSY are measured in years, a discrete-time hazard approach is taken (see Kiefer, 1988;
Meyer, 1990; and Narendranathan and Stewart, 1990 , for example). Moreover, the
3 In case of high school dropout, five different definitions of dropout are used in the various studies. see
Kominski (1990).