THE GREATEST OBSTACLE in distance education in the minds of many is the geographical distance separating the instructor and the learner. The concept of transactional distance asserts that the amount geographical separation is not a significant factor in distance education.

Distance education has been around in one form or another for over a hundred years. Correspondence courses, training films, radio, television, and most recently Internet delivered media have all been a part of the history of distance education.

Distance education has used a variety of media over the years.

In the early 1970s Michael Moore came to the conclusion that the two key factors in independent learning are structure and dialog (Moore, 1973). Moore defined structure as "a measure of an educational program's responsiveness to learners individual needs." He defined dialog as "the extent to which, in any educational program, learner and educator are able to respond to each other." Put another way, structure refers to the design of the instructional program while dialog refers to the interaction through communication of the learner and the educator.

A transaction is a mutual exchange between parties. Moore recognized that in a course high in structure, such as a pure lecture course, there is generally little dialog between educator and learner and transactional distance is maximized. Conversely, as dialog is increased, the structure decreases, thereby minimizing the transactional distance between educator and learner.

Saba (Saba & Shearer, 1994) supported this dynamic relationship between structure and dialog by conducting a controlled experimentation. This research supported the concept that the distance between teacher and learner in distance education was not a geographical distance, but a pedagogical distance determined by the balance of structure and dialog.

Instructional designers of distance education should aim for the optimum balance of structure and dialog. It is important to note that there is no magic ratio of structure to dialog that will fit every course. It is the task of the designer to evaluate and plan for dialog and structure as dictated by the nature of the course.

Although it originated in the domain of distance education, the concept of transactional distance carries significant implications for all types of education. An acceptable balance of structure and dialog is key to successful instruction and learning. Care must be taken during the design of instruction to account for this balance.

Related articles in the Encyclopedia of Educational Technology:

Distance Education
Distance Education: The Human Dimension
Learner Control in Web-Based Instruction
The Instructor's Role

Other sites:

distance-educator.com: A wealth of content on current happenings in distance education.

Moore, M.G. 1973. Towards a theory of independent learning and teaching. Journal of Higher Education, 44(9), 661-679

Saba, F. & Shearer, P. (1994) Distance in Education. In David H. Jonassen (Ed.) Handbook of research for educational communications and technology. New York: Macmillan. 
Robert Faust ，Graduate Student