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Clinical research is a systematic method for evaluating the effectiveness of treatment and for establishing a basis for inductive generalizations about intervention. The ultimate goal is to further intellectual progress by contributing to the scientific base of practice through the development of theory. Theories are created out of a need to organize and give meaning to a complex collection of individual facts and observations.

Methods are the means by which we conduct investigations in a reliable and valid way so that we can understand clinical phenomena. But it is theory that lets us speculate on the questions of why and how treatment works, accounting for what we observe. Theories provide the explanations for findings within the context of what is already known from the successes and failures of previous investigations. As we continue to examine observations, we try to create theoretical generalizations to form a basis for predicting future outcomes. Without such explanations we risk having to reinvent the wheel each time we are faced with a clinical problem.

A theory is a set of interrelated concepts, definitions, or propositions that specifies relationships among variables and represents a systematic view of specific phenomena.1 Theories have always been a part of human cultures, although not all theories have been scientific. Philosophy and religion historically have played a significant part in the acceptance of theory. The medieval view that the world was flat was born out of the theory that angels held up the four corners of the earth. Naturally, the men of the day were justified in believing that if one sailed toward the horizon, eventually one would fall off the edge of the earth. Such theories went untested because of a lack of instrumentation and because it was not considered necessary to test that which was already known to be true.

In contrast, scientific theory deals with the empirical world of observation and experience, and requires constant verification. We use theory to generalize beyond a specific situation and to make predictions about what should happen in other similar situations. The validity of these predictions can be tested through research. The purpose of this chapter is to define the elements of theory and to describe mechanisms for developing and testing clinical theories.


Theories can serve several purposes in science and clinical practice, depending on how we choose to use them. Theories summarize existing knowledge, giving meaning to isolated empirical findings. They provide a framework for interpretation of observations. For example, theories of motor learning bring together the results of many separate studies that have examined schedules of practice, types of skills, psychomotor components of performance, and other elements of the learning process. Theories are also used to explain observable events by showing how variables are related. For instance, a theory of motor learning would explain the relationship between feedback and feedforward ...

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