Suppose teachers wished to determine which of two methods of reading instruction was most effective—one that involved 20 minutes of direct instruction in phonics each day throughout the academic year in grade 1 or one that involved the current practice of having the teacher read a book to the class for 20 minutes each day throughout the year in grade 1. Similarly, suppose they wished to determine whether children learn better in a small class (i.e., with 15 students) or a large class (i.e., with 30 students). Finally, suppose they wished to determine whether requiring students to take a short quiz during each meeting of a college lecture class would result in better performance on the final exam than not giving quizzes.
Each of these situations can be examined best by using experimental research methodology in which investigators compare the mean performance of two or more groups on an appropriate test. In experimental research, it is customary to distinguish between the independent variable and the dependent measure. The independent variable is the feature that is different between the groups—for example, whether 20 minutes of time each day is used for phonics instruction or reading aloud to students, whether the class size is small or large, or whether a short quiz is given during each class meeting. The dependent measure is the score that is used to compare the performance of the groups—for example, the score on a reading test administered at the end of the year, the change in performance on academic tests from the beginning of the year to the end of the year, or the score on a final exam in the class. When researchers compare two or more groups on one or more measures, they use experimental research methodology.
EXPERIMENTAL RESEARCH DEFINED
Experimental research is based on a methodology that meets three criteria: (a) random assignment—the subjects (or other entities) are randomly assigned to treatment groups, (b) experimental control—all features of the...