Transactional distance theory was developed in the 1970s by Dr. Michael G. Moore, Distinguished Professor Emeritus of Education at the Pennsylvania State University (Moore, 1980). It is the first pedagogical theory specifically derived from analysis of teaching and learning conducted through technology as opposed to the many theories developed in the classroom. It is considered by some to be one of the few, if not the only, theory in distance education that can be used to test hypotheses. It can be used to frame experiments in tutoring or other learner support activities to assess what change there is in the outcomes of student learning, often judged by student completion (Tait, 2017). Like any theory, the transactional distance model serves as a heuristic device, a means of identifying questions for research and also a very practical instrument to be used in making these difficult instructional design decisions. Description The theory consists of a set of principles and a model that defines the pedagogical aspects of education (as contrasted with others such as management and policy) in three sets of variables. The first set consists of elements describing the structure of what is designed to be learned, the second in the interaction or dialog between teacher and learners when that structured program is implemented, and the third is the idiosyncrasies of each individual learner with priority given to the potential self-management or autonomy of the students who interact with teachers within the designed structure (Moore & Kearsley, 2012). Transactional distance theory states that when an instructional designer makes decisions, these decisions will result in a certain amount of structure, dialog and autonomy. These amounts can be either unwitting consequences of the instructional design process, or the result of conscious instructional design decisions. Regardless, these variables interact to create transactional distance which Michael G. Moore defines as “a psychological and communication space to be crossed, a space of potential misunderstanding between the inputs of instructor and those of the learner.” Thus, the utility of the theory is that it provides guidance to instructional designers as to how to design the course: e.g. how much structure, dialog, and autonomy to build into the course, so as to minimize transactional distances and thereby maximize learning outcomes. Measuring transactional distance A number of researchers have used Moore's theory as the theoretical underpinning for the development of a number of statistically valid and reliable scales to measure