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The biopsychosocial model is a broad view that attributes disease outcome to the intricate, variable interaction of biological factors (genetic, biochemical, etc), psychological factors (mood, personality, behavior, etc.), and social factors (cultural, familial, socioeconomic, medical, etc.). The biopsychosocial model counters the biomedical model, which attributes disease to roughly only biological factors, such as viruses, genes, or somatic abnormalities. The biopsychosocial model applies to disciplines ranging from medicine to psychology to sociology; its novelty, acceptance, and prevalence vary across disciplines and across cultures.
In a 1977 article in Science, psychiatrist George L. Engel called for "the need for a new medical model." Engel later discussed a hypothetical patient, a 55-year-old man sustaining a second heart attack six months after his first. The patient's personality frames his own interpretation of his chest pain and explains his denial of it until his employer grants him permission to seek help. Although his heart attack can be attributed to an arterial blood clot, the wider personal perspective helps to understand that different outcomes may be possible depending on how the person responds to his condition. Subsequently, the patient in the emergency room develops a cardiac arrest as a result of an incompetent arterial puncture. We can analyse this event in wider terms than just a cardiac arrhythmia. It sees the event as due to inadequate training and supervision of junior staff in an emergency room. Thus while "no single definitive, irreducible model has been published,"  Engel's example offers a starting point for broader understanding of clinical practice.
Some thinkers[who?] see the model in terms of causation. Its biological component seeks to understand how the cause of the illness stems from the functioning of the individual's body. Its psychological component looks for potential psychological causes for a health problem such as lack of self-control, emotional turmoil, and negative thinking. Its social part investigates how different social factors such as socioeconomic status, culture, technology, and religion can influence health. However, a closer reading of Engel's seminal paper in the American Journal of Psychiatry (1980) embeds the model far more closely into patient care. It is not just about causation but also about how any clinical condition (medical, surgical, or psychiatric) can be seen narrowly as just biological or more widely as a condition with psychological and social components, which will impinge on a patient's understanding of her condition and will affect the clinical course of that condition.
Drawing on the systems theory of Weiss and von Bertalanffy, Engel describes the commonsense observation that nature is a "hierarchically arranged continuum with its more complex, larger units superordinate on the less complex smaller units." He represents them schematically either as a vertical stack or as a nest of squares, with the simplest at the centre and the most complex on the outside. He subdivides the vertical stack into two stacks. The first starts with subatomic particles and ends with the individual person. The second starts with the person and finishes with the biosphere. The first is an organismic hierarchy, the second a social hierarchy. He then delineates some principles:
The model is based in part on social cognitive theory. It implies that treatment of disease processes, like Type II diabetes and cancer, requires the health care team to address biological, psychological, and social influences upon a patient's functioning.
In a philosophical sense, it states that the workings of the body can affect the mind, and the workings of the mind can affect the body. That means both a direct interaction between mind and body as well as indirect effects through intermediate factors.
The biopsychosocial model presumes that it is important to handle the three together as a growing body of empirical literature suggests that patient perceptions of health and threat of disease as well as barriers in a patient's social or cultural environment appear to influence the likelihood that a patient will engage in health-promoting or treatment behaviors, such as medication taking, proper diet or nutrition, and engaging in physical activity.
While operating from a BPS framework requires that more information be gathered during a consultation, a growing trend in the US, as is already well established in Europe, includes the integration of professional services through integrated disciplinary teams, to provide better care and address the patient's needs at all three levels. As seen, for example in integrated primary care clinics, such as used in the UK, Germany, US Veteran's Administration, U.S military, and Kaiser Permanente, integrated teams may comprise physicians, nurses, occupational therapists, health psychologists, social workers and other specialties to address all three aspects of the BPS framework, allowing the physician to focus on predominantly biological mechanisms of the patient's complaints See also
Psychosocial factors can cause a biological effect by predisposing the patient to risk factors. An example is that clinical depression by itself may not cause liver problems, but a depressed person may be more likely to have alcohol problems and thus liver damage. Perhaps, it is that increased risk-taking that leads to an increased likelihood of disease. Most diseases in BPS discussion are such behaviourally-moderated illnesses, with known high risk factors, or so-called "biopsychosocial illnesses/disorders." An example is Type II diabetes that, with the growing prevalence of obesity and physical inactivity, is on course to become a worldwide pandemic.
For example, approximately 20 million Americans are estimated to have diabetes, with 90% to 95% considered type II.
It is important to note that the biopsychosocial model does not provide a straightforward, testable model to explain the interactions or causal influences by (the amount of variance accounted for) each of the components (biological, psychological, or social). Rather, the model has been a general framework to guide theoretical and empirical exploration, which has amassed a great deal of research since Engel's 1977 article. One of the areas that has been greatly influenced is the formulation and testing of social-cognitive models of health behavior over the past 30 years.
While no single model has taken precedence, a large body of empirical literature has identified social-cognitive (the psycho-social aspect of Engel's model) variables that appear to influence engagement in healthy behaviors and adhere to prescribed medical regimens, such as self-efficacy, in chronic diseases such as Type II diabetes, cardiovascular disease, etc. The models include the Health Belief Model, Theory of Reasoned Action and Theory of Planned Behavior, Transtheoretical Model, the Relapse Prevention Model, Gollwitzer's implementation-intentions, the Precaution-Adoption Model, the Health Action Process Approach, etc.
Some critics point out this question of distinction and a question of determination of the roles of illness and disease runs against the growing concept of the patient-medical tradesperson partnership or patient empowerment, as "biopsychosocial" becomes one more disingenuous euphemism for psychosomatic illness. That may be exploited by medical insurance companies or government welfare departments eager to limit or deny access to medical and social care.
Some psychiatrists see the model as flawed in either formulation or application. Epstein and colleagues describe six conflicting interpretations of what the model might be, and propose that "habits of mind may be the missing link between a biopsychosocial intent and clinical reality."
Psychiatrist Hamid Tavakoli argues that the model should be avoided because it unintentionally promotes an artificial distinction between biology and psychology and merely causes confusion in psychiatric assessments and training programs; also, it ultimately has not helped the cause of trying to destigmatize mental health.
Sociologist David Pilgrim suggests that a necessary pragmatism and a form of "mutual tolerance" (Goldie, 1977) has forced a co-existence of perspectives rather than a genuine "theoretical integration as a shared BPS orthodoxy." Pilgrim goes on to state that despite "scientific and ethical virtues," the model "has not been properly realised. It seems to have been pushed into the shadows by a return to medicine and the re-ascendancy of a biomedical model."
However, a vocal philosophical critic of the model, psychiatrist Niall McLaren, writes:
"Since the collapse of the 19th century models (psychoanalysis, biologism and behaviourism), psychiatrists have been in search of a model that integrates the psyche and the soma. So keen has been their search that they embraced the so-called 'biopsychosocial model' without ever bothering to check its details. If, at any time over the last three decades, they had done so, they would have found it had none. This would have forced them into the embarrassing position of having to acknowledge that modern psychiatry is operating in a theoretical vacuum."
The rationale for this theoretical vacuum is outlined in his 1998 paper and more recently in his books, most notably Humanizing Psychiatrists. Simply put, the purpose of a scientific model is to see if a scientific theory works and to actualize its logical consequences. In that sense, models are real and their material consequences can be measured, but theories are ideas and can no more be measured than daydreams.
Model-building separates theories with a future from those that always remain dreams. An example of a true scientific model is longer necked giraffes reach more food, survive at higher rates, and pass on this longer neck trait to their progeny. That is a model (natural selection) of the theory of evolution. Therefore, from an epistemological stance, there can be no model of mental disorder without first establishing a theory of the mind. McLaren does not say that the biopsychosocial model is devoid of merit, just that it does not fit the definition of a scientific model (or theory) and does not "reveal anything that would not be known (implicitly, if not explicitly) to any practitioner of reasonable sensitivity." He states that the biopsychosocial model should be seen in a historical context as bucking against the trend of biological reductionism, which was (and still is) overtaking psychiatry. Engel "has done a very great service to orthodox psychiatry in that he legitimised the concept of talking to people as people."
In short, even though it is correct to say that sociology, psychology, and biology are factors in mental illness, simply stating that obvious fact does not make it a model in the scientific sense of the word.
The Tufts psychiatry professor and author S. Nassir Ghaemi considers Engel's model to be anti-humanistic and advocates the use of less eclectic, less generic, and less vague alternatives, such as William Osler's medical humanism or Karl Jaspers' method-based psychiatry.