Designing an outcome study is easier if the clinician has a way to organize observations and hypotheses about those observations. Theories and models help to describe hypothesized relationships among observations or constructs. In all systematic inquiry, a description of the theory or model that is being tested is useful for interpreting the data analysis. This chapter describes what a model is, reviews the variety of disablement models that appear in the physical therapy literature, and highlights the challenges in integrating theories with clinical practice and research.
Theories describe relationships among concepts, structures, or phenomena. A model is a graphic or physical representation of a theory. It might represent the orientation of physical elements (such as a model of a carbon molecule), the relationship of concepts (such as a food pyramid), or the order of a process (such as the Krebs cycle). Theories help to organize and explain observations; models provide a visual representation of relationships.
Models are graphic descriptions of relationships.
Models also provide categories for classifying observations. Each section of a model is operationally defined, such that each section or part is mutually exclusive of other parts. Operational definitions define categories and variables for their unique applications in a study (Portney & Watkins, 2000) and allow the user to sort information into the appropriate parts of a model. For example, the Nagi Model of Disablement has four parts: pathology impairments, functional limitations, and disabilities. Patient problems can be classified according to the operational definitions for this model, and theories about the relationship of impairments to functional limitations or disabilities can be generated and tested through intervention.
Models provide structure for classification of observations.
Models allow users to speak the same language and to classify information in the same way across many settings. When clinicians agree to use a specific model, they are agreeing to use the operational definitions as created by the originator of the model. By using the same definitions of terms, the observations, processes, or events unique to one setting or patient can be combined or compared with those from other clinicians or settings.
Models provide a common language across settings.
Several models of disablement have been created to describe the relationship of disease or injury to the consequences of the disease or injury. These models are presented to highlight the differences in terminology that are used to describe the disablement process; in some cases, the same word is found in different models and defines very different concepts. There ...