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The information that is used to make clinical decisions and to support clinical research can be acquired in many different ways. As one participates in the pursuit of knowledge, it is interesting to reflect on the sources of information that guide our thinking and decision making. How do we decide which test to perform, which intervention will be most successful, which patients have the best chance of responding positively to a given treatment? Oftentimes clinical problems can be solved on the basis of scientific evidence, but in many situations such evidence does not exist or is not directly applicable. It is important, then, to consider how we come to "know" things, and how we can appropriately integrate what we know with available evidence as we are faced with clinical problems (see Figure 1.3).
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As members of an organized culture, we accept certain truths as givens. Something is thought to be true simply because people have always known it to be true. Within such a belief system, we inherit knowledge and accept precedent, without need for external validation. Rehabilitation science is steeped in tradition as a guide to practice and as a foundation for treatment. We have all been faced with clinical, administrative or educational practices that are continued just because "that is the way they have always been done."
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Tradition is useful in that it offers a common foundation for communication and interaction within a society or profession. Therefore, each generation is not responsible for reformulating an understanding of the world through the development of new concepts. Nevertheless, tradition as a source of knowledge poses a serious problem in clinical science because many traditions have not been evaluated for their validity, nor have they been tested against potentially better alternatives. Sole reliance on precedent as a reason for making clinical choices generally stifles the search for new information, and may perpetuate an idea even when contrary evidence is available.
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We frequently find ourselves turning to specialized sources of authority for answers to questions. If we have a problem with finances, we seek the services of an accountant. If we need legal advice for purchasing a home, we hire a real estate lawyer. In the medical profession we regularly pursue the expertise of specialists for specific medical problems. Given the rapid accumulation of knowledge and technical advances and the need to make decisions in situations where we are not expert, it is most reasonable and natural to place our trust in those who are authoritative on an issue by virtue of specialized training or experience.
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Authorities often become known as expert sources of information based on their success, experience or reputation. When an authority states that something is true, we accept it. As new techniques are developed, we often jump to use them without demanding evidence of their scientific merit, ignoring potential limitations, even when the underlying theoretical rationale is unclear.69,70 Too often we find ourselves committed to one approach over others, perhaps based on what we were taught, because the technique is empirically useful. This is a necessary approach in situations where scientific evidence is unavailable; however, we jeopardize our professional responsibility if these techniques are not critically analyzed and if their effects are not scientifically documented.
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The danger of uncritical reliance on authoritative canon is well illustrated by the unyielding belief in the medical tenets of Galen (a.d. 138–201), whose teachings were accepted without challenge in the Western world for 16 centuries. When physicians in the 16th and 17th centuries began dissecting human organs, they were not always able to validate Galen's statements. His defenders, in strict loyalty and unwilling to doubt the authority, wrote that if the new findings did not agree with Galen's teachings, the discrepancy should be attributed to the fact that nature had changed!71
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The trial and error method of data gathering was probably the earliest approach to solving a problem. The individual faced with a problem attempts one solution and evaluates its effects. If the effects are reasonably satisfactory, the solution is generally adopted. If not, another solution is tried. We use this method when we have no other basis for making a decision. We have all used trial and error at one time or another in our personal lives and in professional practice. Trial and error incorporates the use of intuition and creativity in selecting alternatives when one approach does not work.
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The major disadvantage of trial and error is its haphazard and unsystematic nature and the fact that knowledge obtained in this way is usually not shared, making it inaccessible to others facing similar problems. In situations where a good response is not obtained, a continuous stream of different solutions may be tried, with no basis for sorting out why they are not working.
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Trial and error is by nature extremely time consuming and limiting in scope, for although several possible solutions may be proposed for a single problem, the process generally ends once a "satisfactory" response is obtained. Experience is often based on these solutions, and when similar situations arise, a better solution, as yet untried, may never be tested. Therefore, a clinician using this method should never conclude that the "best" solution has been found.
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Many clinical problems are solved through the use of logical thought processes. Logical reasoning as a method of knowing combines personal experience, intellectual faculties, and formal systems of thought. It is a systematic process that has been used throughout history as a way of answering questions and acquiring new knowledge. Two distinctive types of reasoning are used as a means of understanding and organizing phenomena: deductive and inductive reasoning (see Figure 1.4).
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Deductive reasoning is characterized by the acceptance of a general proposition, or premise, and the subsequent inferences that can be drawn in specific cases. The ancient Greek philosophers introduced this systematic method for drawing conclusions by using a series of three interrelated statements, called a syllogism, containing (1) a major premise, (2) a minor premise and (3) a conclusion. A classic syllogism will serve as an example:
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All living things must die. [major premise]
Man is a living thing. [minor premise]
Therefore, all men must die. [conclusion]
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In deductive reasoning, if the premises are true, then it follows that the conclusion must be true. Scientists use deductive logic by beginning with known scientific principles or generalizations, and deducing specific assertions that are relevant to a specific question. The observed facts will cause the scientist to confirm, to reject or to modify the conclusion. The greater the accuracy of the premise, the greater the accuracy of the conclusion.
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For example, we might reason that exercise will be an effective intervention to prevent falls in the elderly in the following way:
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Impaired postural stability results in falls.
Exercise improves postural stability.
Therefore, exercise will decrease the risk of falls.
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This system of deductive reasoning produces a testable hypothesis: If we develop an exercise program for individuals who have impaired stability, we should see a decrease in the number of falls. This has been the basis for a number of studies. For example, Wolf and colleagues72 used this logic as the theoretical premise for their study comparing balance training and tai chi exercise to improve postural stability in a sample of older, inactive adults. Carter and coworkers73 designed an exercise program aimed at modifying risk factors for falls in elderly women with osteoporosis. Similarly, Barnett et al.74 studied the effect of participation in a weekly group exercise program over one year on the rate of falling in community dwelling older people. All three studies found that the exercise groups either had a lower incidence of falls or delayed onset of falls, supporting the premise from which the treatment was deduced.
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Of course, deductive reasoning does have limitations. Its usefulness is totally dependent on the truth of its premises. In many situations, the theoretical assumptions on which a study is based may be faulty or unsubstantiated, so that the study and its conclusions have questionable validity. In addition, we must recognize that deductive conclusions are only elaborations on previously existing knowledge. Deductive reasoning can organize what is already known and can suggest new relationships, but it cannot be a source of new knowledge. Scientific inquiry cannot be conducted on the basis of deductive reasoning alone because of the difficulty involved in establishing the universal truth of many statements dealing with scientific phenomena.
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Inductive reasoning reflects the reverse type of logic, developing generalizations from specific observations. It begins with experience and results in conclusions or generalizations that are probably true. This approach to knowing was advanced in the late 16th century by Francis Bacon, who called for an end to reliance on authority as absolute truth. He proposed that the discovery of new knowledge required direct observation of nature, without prejudice or preconceived notions.75 Facts gathered on a sample of events could lead to inferences about the whole. This reasoning gave birth to the scientific approach to problem solving, and often acts as the basis for common sense. For example, we might observe that those patients who exercise do not fall, and that those who do not exercise fall more often. We might then conclude, through induction, that exercise will improve postural stability.
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Inductive reasoning has its limitations as well. The quality of the knowledge derived from inductive reasoning is dependent on the representativeness of the specific observations used as the basis for generalizations. To be absolutely certain of an inductive conclusion, the researcher would have to observe all possible examples of the event. This is feasible only in the rare situations where the set of events in question is very small, and we therefore find ourselves relying mostly on imperfect induction based on incomplete observations. In the preceding example, if we observe the effects of exercise on a sample of elderly persons, and if balance and exercise responses are related to aging, our conclusion may not be a valid one for younger individuals.
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Even with these limitations, the process of logical reasoning, both deductive and inductive, is an essential component of scientific inquiry and clinical problem solving. Both forms of reasoning are used to design research studies and interpret research data. Introductory statements in research articles often illustrate deductive logic, as the author explains how a research hypothesis was developed from an existing theory of general body of knowledge. Inductive reasoning is used in the discussion section of a research report, where generalizations or conclusions are proposed from the data obtained in the study. Even though imperfect induction does not allow us to reach infallible conclusions, it is the clinical scientist's responsibility to evaluate critically the validity of the information and to draw reasonable conclusions (see Box 1.2). These conclusions must then be verified through further empirical testing.
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The following statement, attributed to Galen, illustrates the potential for the abuse of logic:
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All who drink of this remedy recover in a short time, except those whom it does not help, who all die. Therefore, it is obvious that it fails only in incurable cases.71
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The Scientific Method
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The scientific method is the most rigorous process for acquiring new knowledge, incorporating elements of deduction and induction in a systematic and controlled analysis of phenomena. The scientific approach to inquiry is based on two assumptions related to the nature of reality. First, we assume that nature is orderly and regular and that events are, to some extent, consistent and predictable. Second, we assume that events or conditions are not random or accidental and, therefore, have one or more causes that can be discovered. These assumptions allow us to direct clinical thinking toward establishing cause-and-effect relationships so that we can develop rational solutions to clinical problems.
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The scientific approach has been defined as a systematic, empirical, controlled and critical examination of hypothetical propositions about the associations among natural phenomena.1 The systematic nature of research implies a sense of order and discipline that will ensure an acceptable level of reliability. It suggests a logical sequence that leads from identification of a problem, through the organized collection and objective analysis of data, to the interpretation of findings. The empirical component of scientific research refers to the necessity for documenting objective data through direct observation. Findings are thereby grounded in reality rather than in personal bias or subjective belief of the researcher.
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The element of control, however, is the most important characteristic that sets the scientific method apart from the other sources of knowledge. To understand how one phenomenon relates to another, the scientist practitioner must attempt to control factors that are not directly related to the variables in question. Clinical problems such as pain, functional disability, cognitive dysfunction, deformity, cardiopulmonary insufficiency or motor control concern highly complex phenomena and often involve the effects of many interacting factors. Investigators must be able to control extraneous influences to have critical confidence in research outcomes. This important concept is explored in greater detail in Chapter 9.
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BOX 1.2 The Logic of the Frog

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A commitment to critical examination means that the researcher must subject findings to empirical testing and to the scrutiny of other scientists. Scientific investigation is thereby characterized by a capacity for self-correction based on objective validation of data from primary sources of information. This minimizes the influence of bias, and makes the researcher responsible for logical and defensible interpretation of outcomes.
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Limitations of the Scientific Method
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Although scientific research is considered the highest form of acquiring knowledge, it is by no means perfect, especially when it is applied to the study of human behavior and performance. The complexity and variability within nature and the environment and the unique psychosocial and physiological capacities of individuals will always introduce some uncertainty into the interpretation and generalization of data. These issues differentiate clinical research from laboratory research in physical and biological sciences, where environment and even heredity are often under complete control. This does not mean that the scientific method cannot be applied to human studies, but it does mean that clinical researchers must be acutely aware of extraneous influences to interpret findings in a meaningful way. Some clinical findings may actually be strengthened by the knowledge that patients generally improve with certain treatments despite physiological and environmental differences.