(1) differences in what various estimates are designed to accomplish, (2) differences in the conceptual and technical definition of both the numerator and the denominator used to calculate the rates, and (3) differences in the accuracy of the data used to produce them. Understanding these three sources of differences is key to making sense of the resulting rates.
This chapter first discusses the different purposes of the estimates and the sources of data used in calculating the rates. We then discuss the different types of rates that can be calculated. We close the chapter by discussing the importance of aligning the choice of a rate with the purpose it will serve. The chapter draws extensively from papers prepared for the workshop by Rob Warren, with the University of Minnesota, and Elaine Allensworth, with the Consortium on Chicago School Research (Allensworth, 2008; Warren, 2008).
One major source of differences in estimates of dropout and completion rates is the question they were designed to answer. Analysts operationalize high school completion and dropout rates in different ways because they have different conceptual or practical reasons for making those measurements. There are three chief uses of high school completion and dropout rates.
The first use is to describe the amount (or lack) of human capital in a population. In this case, the rates characterize an attribute of society: they quantify the share of people who bring particular credentials and skills to the labor force. The second use is to describe the “holding power” of schools. In this case, the rates answer questions about schools; they characterize their success at moving young people from the first day of high school to successful completion (see Hartzell, McKay, and Frymier, 1992). The third use is to describe students’ success at navigating high school from beginning to end. For this purpose, the rates answer questions about individual students themselves; they measure how successful students are in progressing from the first day of high school to successful completion.
If the goal of the rate is to describe the amounts of human capital in a population, the timing of high school completion—how long ago or at what age people completed high school—is not of critical importance. Nor, for some purposes, does it matter exactly how young people complete high school—by obtaining a diploma, a General Educational Development (GED) credential, or a certificate of completion, completing an adult education program, or some other way. For other purposes, however, how students complete high school is critical because research suggests that students who fail to earn a regular high school diploma are less competitive in the labor market compared with graduates (Heckman and Rubinstein, 2001; Tyler, 2003). Any young person who has completed high school is considered to have acquired marketable capital, regardless of his or her age at the time of crossing that educational threshold.