One widely accepted aim of evaluation is to assess the merits of educational and social programs that are designed to improve the welfare of people, organizations, and society (Shadish, Cook, and Leviton, 1991). Evaluation also provides meaningful information for making decisions about programs and related policies (Cronbach, 1963; House, 1980; Patton, 1997; Stufflebeam and Shinkfield, 1985; Worthen and Sanders, 1973). Thus, evaluation is often thought of as a pragmatic, or professional, field rather than an academic one.
The two categories—professional and academic—are distinguished by their principal purposes. Academic fields (for example, mathematics) strive to advance knowledge, whereas professional fields (for example, law or medicine) have more practical objectives. A primary goal of an academic field is to test theory (knowledge), whereas a primary goal of a practical field is to question and determine the applicability of basic theories to practical situations (for example, Shadish, Cook, and Leviton, 1991). Because the goal of academic fields is to test knowledge, their theories are descriptive in nature—that is, they are empirically derived. In practical fields, prescriptive theories evolve and are enhanced by descriptive theories, and thus describe the application of knowledge.
Alkin and Ellett (1985) make a distinction between the uses of prescriptive and descriptive theories of evaluation. They state that prescriptive theories identify the essential elements guiding evaluation practice, which suggest the “proper” approach for conducting evaluation. These elements include the focus and role of the evaluation, the specific evaluation questions to be studied, the evaluation design and implementation, and the use of evaluation results (Shadish, Cook, and Leviton, 1991). The various prescriptive theories emphasize, prioritize, and combine these elements differently.
In contrast, descriptive evaluation theories are empirical and provide statements and generalizations that explain evaluation activities (Alkin and Ellett, 1985). Empirically derived descriptive models are central to the advancement of prescriptive theories. This is because prescriptive theories are largely conceptual, and empirical studies help develop an understanding of when a particular theory is suitable, how it functions best, and what it can be expected to accomplish and under what conditions (Cousins and Earl, 1999). Yet with the exception of a few focal areas in the evaluation
I wish to acknowledge the chapter authors for their time and thoughtful contributions. I am also grateful to Jennifer C. Greene for her encouragement and helpful guidance in developing this issue.