Every theory serves, in part, as a research directive. The empirical outcomes of research can be organized and ordered to build theories using inductive reasoning. Conversely, theories must be tested by subjecting deductive hypotheses to scientific scrutiny. The processes of theory development and theory testing are represented in the model shown in Figure 2.1. It integrates the concepts of inductive and deductive reasoning as they relate to the elements of theory design.
BOX 2.1 Ancient Medical Theory: The Four Humours
Originating in the work of Aristotle and Hippocrates, traditional medical theory from Greco-Roman times through the Middle Ages was based on the belief that the body was made up of four elemental liquids: blood, yellow bile, black bile and phlegm. Physical and mental health depended on a balance of these humours, called eucrasia. An imbalance of humours, or dyscrasia, was believed to be the cause of all diseases.
Each humour corresponded to one of the four elements, specific seasons, qualities and personalities. Blood was associated with air, spring, hot and moist, and a sanguine temperament—amorous, happy, generous, and optimistic. Black bile was associated with earth, autumn, cold and dry, and a melancholic personality—introspective, sentimental and lazy. Yellow bile was paired with fire, summer, hot and dry, and a choleric disposition—vengeful, violent and easily angered. And phlegm was linked to water, winter, cold and moist, and a phlegmatic temperament—calm, unemotional and dull.
This theoretical context was used as the basis for diagnosis and treatment, geared toward identifying and pushing out a harmful surplus of a humour. For example, if someone had a fever, they were thought to have too much blood in their body, which was therefore treated by blood letting. Sweating from a fever was considered hot and wet, and foods were given that were associated with cold and dry. The baby with "cholic" was thought to be constantly angry. Epilepsy was believed to be due to phlegm blocking the airways that caused the body to thrash about to free itself. Manic behavior was due to bile boiling in the brain. Black bile was associated with melancholy.
In every era, our theories grow to meet the state of knowledge and science. The humours replaced the theory that health could be explained by divine intervention. Many of the practices associated with the four humours were still part of mainstream medicine in the late 1800s. You can undoubtedly see the connections between the four personalities and many words we use today to describe physical and mental states.
Sources: Four humours. Wikipedia. <http://en.widipedia.org/wiki/Four_bodily_humours>; The Four Humours. Kheper website. <http://www.kheper.net/topics/typology/four_humours.html>; Warren P. The Roots of Scientific Medicine. Hippocrates on the Web. http://www.umanitoba.ca/faculties/medicine/units/history/notes/roots/index.html> Accessed May 15, 2007.
Image of a woodcut from an 18th-century text by Johann Kaspar Lavater.
When we speak of testing a theory, we should realize that a theory itself is not testable. The validity of a theory is derived through the empirical testing of hypotheses that are deduced from it and from observation of the phenomenon the theory describes. The hypotheses predict the relationships of variables included in the theory. The results of research will demonstrate certain facts, which will either support or not support the hypothesis. If the hypothesis is supported, then the theory from which it was deduced is also supported.
When we compare the outcomes of individual research studies with predicted outcomes, we are always aware of the potential for disconfirmation of the underlying theory. In essence, the more that research does not disconfirm a theory, the more the theory is supported. This may sound backwards, but in actuality we can never "prove" or "confirm" a theory. We can only demonstrate that a theoretical premise does not hold true in a specific situation. When a research hypothesis is tested and it is not rejected, that is, the study turns out the way we expected, we cannot state that the underlying theory is definitely true. To make such a statement, we would have to verify every possible application of the theory and demonstrate that the outcomes were absolutely consistent. As this is not feasible, we can only interpret individual hypotheses and conclude that a theory has not been disproved.
Utilization of Theory in Research and Practice
Clinicians are actually engaged in theory testing on a regular basis in practice. Theories guide us in making clinical decisions. Specific therapeutic modalities are chosen for treatment because of expected outcomes that are based on theoretical assumptions. Treatments are modified according to the presence of risk factors, based on theoretical relationships. Therefore, the theory is tested each time the clinician evaluates treatment outcomes. When a theory is used as the basis for a treatment, the clinician is, in effect, hypothesizing that the treatment will be successful. If results are as expected, the theory has been supported. When evidence is obtained that does not support a theory, or that cannot be explained by the theory, alternative explanations must be considered. There may be reason to question how measurements were taken and how concepts were defined, to determine if these were truly consistent with the theory's intent. The validity of the theory may be questioned, or the application of the theory to the specific problem being studied may need to be re-evaluated. It may also be necessary to re-examine the theory and modify it, so that it does explain the observed outcome. If this is not practical, a new theory may need to be considered that will encompass this and all previous observations.
As an example of the application of theory to clinical decision making, Mueller and Maluf20 have described physical stress theory, which states that changes in levels of physical stress cause a predictable adaptive response in all biological tissue. According to this premise, stresses less than normal will result in decreased tolerance of tissues to subsequent stresses, and stresses greater than normal will result in increased tolerance. If we accept this premise, we can assume that when muscle is not sufficiently stressed (not exercised), we would predict decreased tension and power (weakness), which would limit the muscle's future tolerance to outside forces. When muscle is challenged at high stresses (as through exercise), we will see increases in contractile strength. Stresses at either extreme will cause the tissue to fail. When stresses are absent, the muscle will atrophy; when stresses are excessive, the muscle will be strained.
We can use this theory to help with decision making when an individual's muscle performance does not fall within normal limits. As shown in Figure 2.4, for a condition of weakness, due to prolonged low stress levels, the threshold for adaptation will decrease. Therefore, a patient who has a weakened muscle is likely to suffer an injury at a lower force threshold than someone who is stronger. Similarly, a weakened muscle will increase in strength with a lower level of exercise than a stronger muscle would require. This theory goes beyond this specific example, to demonstrate how intrinsic and extrinsic factors can modify the adaptive responses of various tissues. The authors clearly illustrate how continued testing of the theory and its relationships is needed to contribute to the foundations of practice.20
Representation of the physical stress theory, illustrating the effect of prolonged low stress on biological tissue. Low stress results in a lower threshold for subsequent adaptation and injury. Although relative thresholds remain the same, the absolute magnitude of physical stress is lower for each threshold. Injury (and all other adaptations) occurs at a lower level of physical stress than required previously. (From Mueller MJ, Maluf KS. Tissue adaptation to physical stress: A proposed "Physical Stress Theory" to guide physical therapist practice, education, and research. Phys Ther 2002;82:383–403, Figure 2, p. 387. Reprinted with permission of the American Physical Therapy Association.)
Theory as a Foundation for Understanding Research
Understanding clinical phenomena cannot be achieved in a single study. It is a process within a community of researchers involving discussion, criticism and intellectual exchange to analyze the connection between new and previous findings and explanations. This type of exchange allows the inconsistencies to surface, to identify findings that cannot be explained by current theories. This process can serve as a catalyst for a paradigm shift, or a change in the basic framework that governs the way knowledge is pursued.21 For instance, the focus on outcomes in research represents a paradigm shift in rehabilitation science, as constructs such as disability and quality of life become a major focus, rather than the traditional emphasis on changes in physical impairments.22 The ICF is another example, allowing interactions with theories of self-efficacy and health behaviors, and incorporating environmental factors as influences on performance.23 By looking at outcomes in this way, researchers recognize that questions and their underlying theories will take a different direction than in the past.
The importance of theory for understanding research findings is often misunderstood. Whenever a research question is formulated, there is an implicit theory base that suggests how the variables of interest are related. Unfortunately, many authors do not make this foundation explicit. Empirical results are often described with only a general explanation, or an admission that the author can find no explanation. It is the author's responsibility, however, to consider what is known, to examine potential relationships, and help the reader understand the context within which the results can be understood. It is incumbent upon all researchers to project their expectations into the realm of theory, to offer an interpretation of findings, and thereby contribute to the growth of knowledge.24