Biopsychosocial model introduction.

On this page, I introduce the biopsychosocial model of illness. The development of this model in the1970s was, in my opinion, the most advance having the most significant influence on rehabilitation since rehabilitation emerged as a speciality after the First World War. It led to the World Health Organisation’s International Classification of Impairments, Disabilities and Handicaps (1980; WHO ICIDH) and, alter, the International Classification of Functioning (2000; WHO ICF). The use of the model underlies many effective rehabilitation interventions. Yet, disappointingly, it is still scarcely known outside the fields of rehabilitation and psychiatry. It is not difficult to understand – I use it regularly when talking to patients and families, and they understand it. This page will introduce it, contrasting it to the 400-year-old biomedical model of illness. Other pages shown at the end will explore the model’s power in various areas of healthcare practice.

Table of Contents


Which of your possessions that do something can you repair when they break down? How do they differ from those you do not even attempt to get working? The difference will be that you understand how they work, albeit incomplete. You appreciate the working relationships between the different parts and what effect a problem in one element might have on overall function. You have an internalised model of how it works, which you use to analyse what might be dysfunctional and to predict the effect of a change you might make. You use models all the time. How does the check-out in a supermarket work? How do you order food in this cafe in Italy? What will happen if I cut that piece of wood? Using a good model will lead to better outcomes. We need the best available model for rehabilitation.

This page will explore the importance of health models and what models there are. It will contrast the two models most widely used within healthcare; it will not consider the public’s numerous models. This introduction will then lead to an explanation of the biopsychosocial model of illness.

What is a model?

Most people are probably unaware that they have any ‘model of illness’. And few could explain what model they have. Yet, from an early age, we all develop and use a model of illness. So first, what is a model?

When your car starts to malfunction, your immediate thoughts include why has this happened, why now, what is wrong, what will happen if I ignore it, and what can I do about it. Your answers will depend upon your understanding of how your car works. You may understand all about the engine (diesel, petrol, or electric) and other vehicle mechanics, or you may know very little. Most people know that fuel is needed and will check that. Some people will automatically check the oil level, radiator fluid, or something else because that was the problem last time.

Eventually, most people will go to a garage because the engineers have a better model of how cars work and will know the details of each different type of car. The reality is that now few people have a sufficiently detailed model of how cars work and malfunction in their minds to analyse the problem and find a solution. Engineers, on the other hand, have excellent models.

In other words, a model refers to the representation in the mind of some object or process or activity that you use to analyse how changing one factor might alter the situation. A model helps identify the best action to improve a situation or solve a problem. For example, when talking to someone, you will have a ‘model’ that helps you predict how they will respond to a request or remark. If you want them to do something, you might think through their response to one way of asking, then another, until you find the approach most likely to succeed. Using a model, you can predict what action is most likely to achieve your goal.

Why a model of illness?

You are a conscious being, which means that you have a personal awareness of what sensations you are feeling, of the quality of your performance of activities, and your emotional state. You can compare your experience or performance against what you would expect. At some point, you may notice something unexpected, such as being more short of breath than expected or experiencing pain without good reason. If the unexpected phenomenon continues, or if the difference is severe or very significant, you will start to analyse it.

Research shows that, when faced with an unexpected bodily or personal experience, people ask much the same questions in all cultures (here):

  • What. What is the immediate, direct cause for the unexpected experience?
  • Why. What factors or events led to this experience occurring now?
  • How. How does the cause lead to the change or experience?
  • Future. What will happen over the next minutes, hours, days, weeks?
  • Action. What can I do, or what can others do, to lessen any consequences?

Each person will have their explanatory model of illness. Some people will attribute most changes to allergy, diet, or electric fields. Others, now and in the past, will attribute experiences to enemies cursing them or casting evil spells. Whoever we are, we will have a preferred and more likely way of analysing unexpected bodily function.

Healthcare is different. Chaos would reign if each person involved with a patient used a different model, giving other explanations, prognoses and treatments. Healthcare organisations and the society in which they function must have a shared model accepted as the basis for decisions. A person may still have a different model. They can choose to ignore healthcare, or they can choose to take some of the offered explanations etc., if only sceptically.

Society needs a single model on which to base societal decisions such as who is ill and eligible for sickness benefits, who will get treatments, and how do we organise services. The health services also need a single model to have a common language and a standard set of approaches to a problem.

Thus we all need and use a model of illness, and these models differ, but all must also use a socially accepted model to guide the societal response to disease. The biomedical model is the current socially dominant model.

The biomedical model

Although everyone’s model differs, in most modern Western cultures, and increasingly elsewhere, a biomedical model is a socially dominant model. The essential, critical features of the biomedical model, sometimes referred to as “the medical model”, is that:

  • all illness is due to disease,
    • disease is located within the body;
    • and all abnormal experiences are symptomatic of disease
  • disease occurs outside the control of the patient
  • treatment, and cure, is achieved by external agents (drugs, surgery etc)
    • and cure will reverse illness and return the person to health

This model is closely associated with several other cultural phenomena:

  • a reductionist, scientific approach;
    • for example one disease accounts for all abnormal experiences
  • a social ‘contract’ whereby the ill person
    • is expected to seek expert help as soon as possible
    • is excused of some or all social responsibilities
    • is expected to strive to return to health as quickly as possible
  • a complete separation between mental and physical phenomena

This model, at present, is the basis for almost all political and management decisions made about healthcare and is the basis for most funding decisions and policies. It is so ingrained that it is not discussed or mentioned anywhere. Indeed, it is hard to find any definition or discussion. Among the first articles identified by Google on a search for “The biomedical model of illness” is one by me and Peter Halligan, writing about the biopsychosocial model. (here) There is no definitive text, and indeed the model is barely mentioned in health textbooks, political discussion documents or any other writing on health and illness. It is so ingrained no one notices that they are using it.

Why is a new model needed?

This biomedical model arose in the early 1500s when the scientific revolution started, and over the next 400 years, it evolved as scientific knowledge grew. It was very successful and led to great advances. However, early in the 1900s, disquiet began (here), particularly around the separation of mental health. Then, over the twentieth century, other developments occurred, which drew attention to weaknesses I have discussed here. Among other developments were:

  • the arrival of holism (1932), developing with general systems theory and the recognition of complexity;
  • the development of sociology, and the recognition of the influence of culture on illness and behaviour;
  • the increasing recognition of the social, environment and financial influences on illness and health;
  • more recently the emergence of multi-morbidity, where patients often have multiple long-term diseases;
  • and the recent recognition of functional disorders and the major influence of mental health on bodily function and personal behaviour.

There are many weaknesses in the model and its associated cultural aspects.

Psychologically-based illness.
The assumption that all illness is secondary to damage within the body became increasingly untenable as psychiatric illnesses were recognised and delineated. Though some had visible causes, such as General Paralysis of the Insane (syphilis), conditions such as depression, manic-depressive psychosis, obsessive disorders, and anxiety did not have any detectable structural cause. One solution was postulating biochemical abnormalities (chemical imbalances) and other physical causes. This approach was associated with electro-convulsive therapy, insulin coma treatment, and leucotomies. The biomedical model is of no practical value when analysing or managing psychological illness.

Psychological consequences of disease.
The biomedical model cannot explain the apparent interrelationship between being ill, having a psychological reaction to being sick, and the effect of emotional and other changes on the illness and matters such as disability and symptoms.

Functional disorders.
Functional disorders account for about 25% of all hospital outpatient attendances and perhaps 5% inpatient bed use. Despite this, medical students were taught little or nothing about them for many years. More worryingly, many doctors did not recognise them, and many of those who did dismissed the patients as not being ill. Until recently, there were no services for people with functional disorders, and they cannot be coded in most healthcare statistics. They are “the elephant in the room” – a whole herd!

The biomedical model identifies when someone has two or more conditions. Still, it cannot analyse the interrelationships between the different diseases to estimate their contribution to a patient’s overall problems. The treatment model associated with the biomedical model also is inadequate and may lead to the overuse of treatments.

The basis for funding.
Initial attempts to base payment on diagnosis rapidly failed and led to increasingly complex mechanisms to adjust payments such as Diagnosis Related Groups (DRGs). Disease-based fees could not be used in intensive care units and could not manage patients with functional disorders. More importantly, the actual disease diagnosis has only a weak relationship to cost. Most resource in hospital is attributable to the care needs of a patient, which arises from their disability and behaviour.

The basis for health management information.
The health service collects data on the disease through the International Classification of Diseases (ICD). It contains virtually no information on clinically essential matters such as incontinence, confusion, lost mental capacity, or unconsciousness. Routine hospital data cannot reveal how many patients leave the hospital unable to care for themselves, urinary incontinence, inability to walk upstairs, etc.

The biomedical model of illness does not help manage and resource the health service. It cannot classify about 25% of patients attending hospital outpatients. It provides no information on the need for care and support.

The biopsychsocial model of illness

The original article about the biopsychosocial model of illness was published in Science in 1977 by Engel. However, this was the culmination of work undertaken by many people from many disciplines over many years. The first reference I can find was in an article by Adolf Meyer, an influential psychiatrist, published in the Journal of the American Medical Association in 1917, which refers to a presentation in San Francisco in 1915. His interest probably predated 1915.

In his article, Engel wrote, presciently,” But nothing will change unless and until those who control resources have the wisdom to venture off the beaten path of exclusive reliance on biomedicine as the only approach to health care.” Twenty-seven years later, there was no change; forty years later, little had changed.

The original article, which is well worth reading, was centred on psychiatry and understanding the influence of non-disease factors on health and illness. Examples used included insulin-dependent diabetes and grief. It did not explicitly set the model in the context of rehabilitation.

The framework, the conceptual ideas, was rapidly used by the World Health Organisation to classify the consequences of disease in the International Classification of Impairments, Disabilities and Handicaps (WHO ICIDH, 1980). In the light of much, quite justified, criticism, the framework was improved and published in 2000 as the International Classification of Functioning, Disability, and Health. (WHO ICF).

The WHO ICF added two main improvements. There was a change in terminology, introducing ‘activities’ in place of disability and ‘participation’ in place of handicap. The use of activities emphasises the focus on goal-directed behaviours. The phrase’ limitation of activities’ is also a clear description with no stigma attached. Nonetheless, the word disability is much more well-known and is still used widely. The WHO removed the term, handicap, as it was considered demeaning and carried much stigma. Instead, the WHO introduced the concept of participation (in society). While the emphasis on engaging with social activities is good, the exact meaning of participation is still uncertain, especially when considering how to measure it. (here)(here)

The second change was the addition of contextual factors, including the physical, social, and personal contexts. This change was essential because contextual factors can cause or increase limitations in activities and participation, and changes in contextual factors can influence limitations. The context helps in understanding a person’s activities and participation. More importantly, intervening to alter context is often a potent means of improving a patient’s situation.

The vital point to understand about the WHO ICF is that it uses the biopsychosocial model as a framework to classify the non-disease aspects of illness, including some factors that impact the condition. The WHO ICF is not, in itself, a model. It does not comment on, and it does not document or quantify, the nature or direction of any inter-relationships. I summarise the model in this graphic.

Making the biopsychosocial model holistic

Although Engel’s article acknowledged many factors, including culture, when the model was initially operational in the WHO ICIDH, the WHO limited the consequences of disease described to person-related items. The move to the WHO ICF framework was a significant advance because it incorporated contextual factors, which allowed better interpretation of practical consequences and suggested actions that might reduce the consequence of disease. Nevertheless, the model was still incomplete because some other items were missing.

Over about 10-12 years, my friend and colleague Peter Halligan and I discussed patients for hours most evenings at the end of the working day. In these conversations, I usually framed my contribution within the biopsychosocial model. He would then ask pertinent questions, challenging my model. Our dialogue was productive, culminating in our paper in the British Medical Journal in 2004 (see here), where we added more features and continued this development in 2017.

The latest version of this framework termed the holistic biopsychosocial model, added four features that make it more person-centred.

The first two concern time. People working with adults easily overlook the importance of time, but paediatricians do not. As its foremost consideration, everything in paediatrics has the child’s age. Children change and mature rapidly. Though biological change is slower in adulthood, other contextual aspects vary significantly. Therefore, some consideration of a person’s age, or more accurately, the stage of their life, is critical.

The person’s stage within their particular illness is also an essential factor, and this is the second temporal domain within the framework.

The third and fourth aspects of the model both make the model personal to the specific patient.

The first is choice. We all can choose, and patients make many choices in long-term illnesses. Some of those choices are against medical recommendations. Any model of illness that does not factor in a person’s choice will fail more often than it succeeds.

The second is quality of life, alternatively described as wellbeing. The quantification of this rests entirely with the patient. Only the patient can (a) identify what factors are essential in determining their quality of life and (b) decide what weight or importance to attach to each factor. These weights may well determine the person’s choices.

The addition of these four items returns the model from its original impersonal use in the WHO ICIDH to a much more person-centred framework. It also now includes two items that fall outside the range of items that can, to some extent, be observed or deduced – the quality of life and individual choice. Both these items are determined entirely by the person. The importance they give to items within the model will influence a person’s preferences and judgment of their quality of life. Each person’s choice of items and domains is their own.

A systems model

Finally, we can discuss how the model might help when analysing a situation and predicting the consequences of actions. We can consider the characteristics of the model.

Engel stressed that his model fitted within the realm of General Systems Theory. This theory underlies similar models such as Kielhofner’s Model of Human Occupation. The vital characteristic to note is that the model is highly complex. The key features of a complex system are:

  • multiple factors can influence one factor
  • one factor can influence many others
  • the relationships can be in any direction, or bidirectional
  • the relationships are not linear
  • there are direct and indirect relationships

See here for further discussion of complexity.

A further vital point is that a system (or domain) comprises lower-order units that are also systems. The body consists of organs; organs are composed of cells, many intracellular organelles, etc. At the same time, most systems are one system among other superordinate systems. The person is part of their family; the family is part of a neighbourhood etc. The person may be part of a workgroup; that group may be part of a department; and so on.

In rehabilitation, one cannot hope to collect information on and analyse the effects of all superordinate systems in which a person is involved, nor the interactions between all subordinate systems. The biopsychosocial model provides a framework to collect the different contextual systems that may affect the patient into manageable units. A rehabilitation expert’s skill is to identify the critical factors in a particular case.

And the weaknesses

Some people and articles criticise the biopsychosocial model. Almost all are, in fact, critical of the way it is used or interpreted rather than the model itself. There are also other criticisms made that I have heard but not (yet) seen written.

Use in disability & employment allowance disputes.
There are many articles, some in scientific journals, others in more journalistic publications, which criticise the model for decisions about disabled people and their right to employment or other disability allowances. These criticisms are inherently invalid as the model does not make the decision. It is not the framework that is to blame. The model or framework is intended to help analyse and understand a situation. It cannot itself make any decision.

It may well be that the assessor is undertaking a poor analysis, not recognising the existence of a factor or its ability to have an influence. Alternatively, the assessor may feel that, although factors A, B, and C are present and might cause the observed disability, they (the assessor) believe that the person has chosen to act in a disabled way.

In other words, it is not the model that is faulty. It may be that the analysis is inadequate, perhaps because the assessor does not have an appropriate level of knowledge and/or relevant skills. It may be that the interpretation is wrong or, perhaps more accurately, at variance with the understanding of others. It could be that the assessor is misinterpreting the legal or policy guidance.

Use in analysing some conditions.
The second area of public debate and concern relates to functional disorders, with chronic fatigue syndrome being a particular case in point. I do not wish to take any specific view here but will explain the issues.

Fact one.
About 25% of people attending outpatients do not have any disease that can plausibly account for their prevention problems. A follow-up confirms that few go on to manifest any disease. This problem is often referred to as a functional disorder, and these are well recognised in most medical specialities such as neurology. It is unknown why any particular person may develop such a disorder, but some risk factors are known,

Fact two.
It is one of the defining characteristics of complex systems that can malfunction even when all the individual components function correctly. This phenomenon is a special case of a general property of any system, known as an emergent property. The most obvious example is consciousness. We undoubtedly have consciousness (though its nature is uncertain), but we cannot explain it based on neurophysiological processes within the brain.

One hypothesis is that functional disorders represent an emergent property of the holistic biopsychosocial systems model. Indeed, almost all complex systems experience failures, yet investigation does not find any specific abnormality. Many common examples occur within healthcare when a patient is harmed not through willful behaviour or anyone’s culpable negligence but simply because healthcare is an extraordinarily complex system.

It is people who use this model to understand this class of illness. They do so to identify better treatments, and helpful interventions, such as cognitive behavioural therapy and exercise (being active) are two. These are not cures but ways of improving the life of the patient.

It’s not our responsibility.
A third criticism is that the issues identified “are not our responsibility”. For example, an inpatient rehabilitation team may not be responsible for sorting out housing, organising transport for someone to attend a day centre, helping the person apply for the financial benefits they need, providing the wheelchair they need to get around etc. Does this mean that the team should not ask or be concerned about these matters?

I have no fixed opinion on whether or not any of the examples are or are not the direct responsibility of a specific rehabilitation service, but:

A) I would argue that knowing about these problems is a vital responsibility. Without that knowledge, much of your patient’s behaviour and choices may appear irrational or cussed.

B) I would also argue that, although it may not even be in your power to do something, it is probably in someone’s power, and therefore you need to contact that person or organisation and ask for their input. This action is not only morally correct, but it usually pays off in terms of a more effective period of rehabilitation and a shorter stay because most of the problems will, if not addressed, delay discharge and/or increase the risk of re-admission to an acute hospital,

I conclude that the model is the best available at present. Doubtless, it can be and, I hope, will be improved over the next 40 years. It is much more potent as an analytic tool than the biomedical model or any other model that I am aware of. It includes almost all existing models within it.

More on this site

This model is mentioned throughout the site, but there are some pages and posts that explore different aspects of the model and they are introduced in the pages linked below.

Validity of biopsychosocial model of illness
This long page considers the validity and value of the model. It includes some discussion of what a model is (it is really a theory) and how validity is determined (it is compared with alternatives). It then compares the biopsychosocial theory of illness with the biomedical theory of disease. Then, after discussing the large variety of other models of illness, it considers its usefulness. Finally, it discusses the criticisms of the biopsychosocial theory of illness. Read more here.

Time and the biopsychosocial model.
This page explores the timeframes that apply in each system or domain of the biopsychosocial model. It demonstrates that the longer timeframes associated with disability and rehabilitation are not well served in a healthcare system that runs in the short timescales associated with the disease. To read more, go here.

Patient-centred care.
This page explored the inter-relationship, indeed inter-dependence between being patient-centred and using the biopsychosocial model of illness. It then explored a model of communication, based on the Four Habits approach, and the evidence behind the method. It teaches, briefly, what the method is and what it achieves. See here.

The end

Scroll to Top

Subscribe to Blog

Enter your email address to receive an email each time a new blog post is published. 
Then press the black ‘Subscribe’ button.