Validity of BPS model

BSP = BioPsychoSocial model.
To those who know my abhorrence of abbreviations, I apologise.

So what?” After setting out the biopsychosocial model to medical students, one implicit, and sometimes explicit, comment is “Well, why is this important, and what is its relevance to us as doctors (to be)?” Fortunately for my self-esteem, other students do immediately see its relevance. Nonetheless, it is an important and pertinent question, particularly when you are part-way through a six-year learning and training programme and have so much more ‘factual and scientific’ information to learn.

This page will demonstrate that, compared with the alternative models of illness, the biopsychosocial model is the best. That is not to say that it is perfect, or answers every question. But I do hope to convince you that it is a better theory when analysing illness, whether from a clinical point of view, with an individual patient, or from a broader scientific point of view.

A theory is ..

I have previously referred to the holistic biopsychosocial model, as a ‘model of illness’. This is following the tradition within health, where people refer to ‘the medical model’, usually as something they disagree with.

The term, model, is actually referring to a theory of illness. A theory is “a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained” [Oxford English Dictionary] So the ‘model’ is more accurately referred to as ‘the biopsychosocial theory of illness‘.

A theory is characterised by the fact that it is falsifiable (Popper); it is in principle possible to find a fact that is incompatible with the theory. Einstein’s theory predicted observations that were incompatible with Newton’s theory and, when confirmed, his theory demonstrated its superiority. Newton’s theory was still good enough to get men to the moon and back. It was not wrong, it was incomplete.

The current dominant model is the biomedical model. There is no definitive description written down anywhere. It evolved over 400 years as science developed and evolved.

So what I need to show is that aspects of illness that the biomedical model cannot explain can be explained by the biopsychosocial theory. It is also possible that the biopsychosocial theory will make a prediction about illness that can be (or has been) verified. The slight difficulty in this process is the absence of any definitive description of the biomedical model, other than the ones I have given!

Disease and illness

As will become apparent, the biomedical model is a theory of disease, but it has been used as a theory of illness, and this has led to the problems now facing healthcare systems in most countries. Therefore a short interlude is needed, to explain how disease and illness differ.

Disease refers to a change in the structure and/or function of an organ or organ system within the body. In systems terminology, it is a dysfunction of one of the component systems that, between them, make up a person’s body. The term usually used is pathology. The change, which is usually a deviation from normal for the person concerned, is sometimes but not always associated with manifestations at the level of the body – symptoms or signs.

The biomedical theory evolved as science advanced, and studies of human structure and function in turn led to science advancing. It was a very successful theory.

Illness refers to the personal experience of ‘not being well’. The Oxford English Dictionary’s definition – “a disease or period of sickness affecting the body or mind” – does not really capture its essence. This definition also conflates disease with illness. Many people living with long-term disease do not consider themselves ill. Many people with long-term disability do not consider themselves ill.

The construct of illness encompasses a variety of recognised terms. It is related to, though not the same as, the ‘sick role’. It is akin to ‘not being healthy’. Illness is close to sickness. Sickness is entirely a socially determined state, because being sick leads to the possibility of being absolved temporarily of social responsibilities. Illness is a little more. Someone may feel ill and consider himself ill while society may not agree that he is sick, and able to avail himself of social help.

In other words, illness is a personally-determined state, a feeling that in some way you are not functioning as you should be, or you are experiencing something that is concerning or distressing. In contact, sickness requires society to agree that you are ill. Illness and disease are usually present together, but not inevitably. Some people may feel that they are not unwell, while society may determine that they are sick. A person who has mania, could well be sick but not ill.

Biomedical model:
some failures

The main characteristics of the biomedical theory of illness were given here. It has had great successes over the last 400 years, allowing the identification of many diseases and treatments for some of the diseases. As a theory of disease, it remains strong.

Unfortunately a good theory of disease is very unlikely to be a satisfactory model of illness; indeed it may be harmful. Illness is a personally determined state. It is often precipitated by disease, but it is possible to have disease and not be ill, and it is possible to be ill but not have disease. I will outline some areas where the biomedical model fails and/or causes actual harm.

The biomedical model assumes that disease is either cured, or leads to death. Its development was set within a context of identifying the cause of an illness. It was not developed to consider long-term disease states. Its purpose was entirely focused on discovering the abnormal structure or function, located within the body, that caused illness. Its purpose was never to understand the illness itself.

Chronic disease.

Even when the biomedical model was evolving over the first 300 years, chronic disease was probably quite common. However, for most of the population, it was just one of many difficulties faced. People did not enter a sick role; they had to work and participate in society to live. Beggars may have had a chronic disease, but they were not common.

The biomedical model does not give any useful insight into the management of chronic disease. Chronic disease is outside the theory.

Multiple diseases.

For exactly the same reasons, the biomedical model offers no insight into the management of two or more diseases, particularly when one is chronic. If the two diseases share similar symptoms, then even diagnosis may be difficult. The primary difficulty, however, is that it cannot help determine which disease might be contributing to a disability, nor how great that contribution is.

The biomedical model does not give any useful insight into the management of multiple diseases. Patients with multiple disease are outside the theory.

Psychological disorders.

The biomedical model cannot explain psychologically determined disorders. The model or theory has taken two approaches to this difficulty.

The first was provided by Descartes, who proposed that the mind was a separate phenomenon, simply not part of the body. This led, eventually, to a separation of health services into two branches: mental health services; and the rest, sometimes referred to as acute health services or medical services.

The second approach developed more recently, in the twentieth century, and basically started to consider psychological illnesses as having a basis in altered biochemistry and/or neurophysiology. At its height this theory led to treatments such as leucotomies, and the use of a range of drugs. Indeed the apparent success of drugs was used as evidence that psychological illness was simply another ‘physical’ illness like diabetes. My year of training in psychiatry was in such a department; I had to oversee ‘insulin coma therapy’ (i.e. prolonged hypoglycaemia, over many weeks); I was taught that it was a ‘physical treatment for a physical problem’..

It has become obvious that, although some drugs may give some benefit, the primary causes of much psychological illness and distress are social and contextual. Thus, although conditions such as ‘alcoholism’, anxiety, depression, and phobias have been termed diseases, there is no good evidence to suggest that any unique and specific bodily dysfunction is the proximate cause. This is not to deny that there are genetic and other bodily disorders which can increase the risk of a psychological disorder.

The biomedical model has not given any useful insight into psychological illnesses. It could be argued that it has delayed the acknowledgement of the importance of social and contextual factors, and of psychological and behavioural treatments which are effective.

Psychiatric illnesses.

I am drawing a distinction, which is possibly valid (it is some years since I trained in psychiatry!), between psychological illnesses as above, and psychiatric illnesses which involve delusional beliefs and disordered thinking. These were termed ‘major psychotic illnesses’ when I trained.

As far as I understand, these illnesses are associated with significant changes in brain structure and function. Indeed schizophrenia was initially termed ‘dementia praecox’, early dementia.

Thus these disorders may have a primary bodily abnormality. Nevertheless, it is still clear that social factors have an important influence.

The biomedical model may have given some insight into psychiatric disorders, although probably by accident, but it is unhelpful beyond the diagnosis and does not assist with management, including rehabilitation.

Functional disorders.

The biomedical model simply cannot explain functional disorders. Indeed, the strength of attachment to the biomedical theory of disease probably explains the prolonged failure to recognise that functional disorders ‘exist’ as a legitimate category of illness. Although not named as functional illness, the phenomenon has been recognised for well over 150 years. It was given many, more or less derogatory, names: hysteria, non-organic disease, shell-shock, abnormal sickness behaviour, malingering, somatisation etc.

The reality, which has been obvious to clinicians for all my professional lifetime, and was obvious well before, has only been acknowledged as a valid condition (against much resistance) over the last 25-30 years with active research over 15-20 years at most.

Yet, despite a wide acceptance of the phenomenon, with large and rapidly growing specialist societies, websites, and research projects, there is still active resistance. For example, some patient organisations for some functional disorders still hold to the belief that their condition is actually due to some (yet to be discovered) primary cause for which there will be some (yet to be discovered) cure.

The biomedical model’s contribution to functional disorders has been to delay their recognition and scientific investigation for, possibly, over 100 years. It still contributes to the unwillingness of many patients and many clinicians to accept the reality of the condition, such that many patients are not benefitting from treatments that could help, but not ‘cure’, them.


This section has shown that the biomedical model of illness fails as a model of illness. I am also suggesting that adherence to this model delayed the development of a better understanding of common psychologically-based illnesses. Further, the model is still responsible for some patients failing to gain access to, or use if offered, interventions that may reduce their distress and disability.

Holistic biopsychosocial
theory of illness.

I will now put forward some evidence to show that the biopsychosocial theory of illness is better that the biomedical model. It may not be perfect, but I know no better theory for use in healthcare. There may be complex sociological theories, but they are likely to focus primarily on sociology. Healthcare needs a theory that is philosophically sound, and is practically useful. Particularly, any theory of illness needs to recognise the central role of disease, not as the only relevant factor, but a major factor nonetheless.

Psychological and functional illnesses.

The holistic biopsychosocial theory is based in general systems theory. This aspect of the model was emphasised by George Engel in his original paper. One of the characteristics of systems is that they can malfunction even when none of the individual components is malfunctioning.

What is the first thing you do when your computer freezes. Turn it off and restart it. It works. There was no fault in any part of your complex machine, yet it suffered a malfunction. Dysfunction happens in complex systems.
Hospitals are extremely complex systems. Malfunctions, up to and including so-called ‘never events‘, arise not because any person is acting wrongly, or has any intent to harm. The system just malfunctions despite complex control mechanisms.

People are massively more complex than computers and healthcare systems. The surprise is that we function so consistently and so well. It should not be a surprise that our ‘system’ sometimes malfunctions a little – we call it illness. The majority of malfunction can be traced back to a disease. Many diseases such as tumours are themselves due to system failures within the body. Some diseases are due to external agents, such as a virus.

Research evidence suggests that about 25% of people referred to hospitals as out-patients have functional illness. Other population-based evidence shows that most people experience brief alterations in sensation or other functions which have no explanation. They are so common that they are dismissed as normal. Yet they are probably brief system disturbances.

Psychological disorders – anxiety, depression, phobias, even eating disorders – are also common. Indeed the experience of many of these ‘disorders’ is a common day-to-day experience, and part of life for most people, and only occasionally are they are considered beyond ‘normal’ and so become an illness.

Research also shows that social and personal adverse events or experiences are associated with an increased risk of functional disorders and psychological disorders. One plausible explanation is that these illnesses arise when the demands upon the body (including the brain and psychological functions) exceed capacity, when malfunction (illness) occurs. Past experiences and genetic differences may reduce resilience, making dysfunction more likely.

Whatever the explanation, the fact that psychological and functional illnesses are predicted by, and can be explained using the holistic biopsychosocial model is powerful evidence in support of its validity.

Severity of disease
v. severity of illness.

It is common experience, fully confirmed by research, that severity of disease and tissue damage is only weakly related to severity of an illness, as rated by disability or any other measure. For example the relationship between the size of a cerebral infarct in stroke as assessed acutely does not predict outcome well. Two people with similar fractures (and other injuries) may have different outcomes.

This discrepancy is difficult to explain in the biomedical model. It would be predicted by, and is easily explained by the holistic biopsychosocial theory of illness. There are many factors which moderate the effect of disease severity: family and financial support, employment, past experience, other illnesses and injuries, personal strengths and weaknesses and so on.

A further specific example of validity arises from research into the INTERMED. The INTERMED is a measure of complexity explicitly constructed using the biopsychosocial theory of illness. Research over about 20 years has found that complexity, as measured using the INTERMED, influences long-term outcome and long-term service use in ways that would be predicted.

These two observations show that factors outside disease severity, but present within the biopsychosocial theory, relate to the severity of a patient’s illness in ways that would be expected.

Use of the theory

Theories are usually also validated through use and utility; a good theory is used more than less good theories. In healthcare, many documents and policies, and many organisational structures are written or developed without explicitly using any model. It is likely that the biomedical model has a strong influence in that case.

There are now many examples of the use of the biopsychosocial theory of illness:

  • the World Health Organisation used it to structure the International Classification of Functioning, Disability, and Health;
  • many (UK) guidelines use it, for example for stroke management, multiple sclerosis and traumatic brain injury;
  • it is used when designing and describing most rehabilitation research;
  • its use by the clinical team is mentioned in many research studies showing effectiveness of rehabilitation;
  • many ‘core data sets’ for specific conditions are being developed using the biopsychosocial theory framework to structure data;
  • measures and assessment protocols, discharge summaries, and other patient letters and reports are increasingly structured using the concepts of this theory;
  • it is taught within some (but not all) UK medical student courses.

Personally I have used it in my day-to-day clinical, research, and management and service improvement work since about 1986. I find that patients particularly find it easy to understand.

Moreover, the most recent article I have written has been downloaded 2000 times each month since it was published in July 2017. Its predecessor (no longer available, having been removed by my employers when I retired) was also downloaded at about the same rate for seven years.

The widespread and, now, increasing use of the biopsychosocial theory of illness in many aspects of healthcare suggests it is meeting a need. This is further evidence of its validity.

Other theories, and
criticisms of the theory

A theory enters a competitive market. I have already discussed the model I take to be the major competitor, the biomedical model. There are other models, which I will discuss briefly.

There are also criticisms of the biopsychosocial model of illness. A quick search will find several or many such articles . The criticisms raised will be considered.

Other theories.

There are innumerable model of illness. Some 25-30 years ago a friend reviewed nursing and other models and found a great many. Reviews have been published. Books of some specific models have been published. This section will not be a systematic review. It will illustrate a few generic types of model.

The social model.
This is largely a model or theory of disability, rather that illness. Its main argument is that disability is caused by society through (a) labelling (and stigmatising) and (b) failing to make the community suitable for people who have any impairment. It argues that people are disabled (as a verb) by society.

This theory developed as a counter to the biomedical model, and many of its criticisms of that theory are valid. It is also true that society could do much more to improve the life of people who have any of a wide variety of impairments. The proponents of this model have influenced politics. There are now laws against discrimination, and other regulations that require reasonable adjustments to be made for people who are disabled.

As a theory of disability, it is valid. As a theory of illness, it is weak in that it does not consider disease. It is not much focused on psychological aspects of illness. Most importantly, the ideas are fully incorporated into the biopsychosocial model of illness.

Nursing models.
There were, and probably still are a number of models used within nursing. They largely centre on aspects of illness that specifically concern nurses and nursing – as one might expect. They were not intended to be models of illness.

Model of Human Occupation.
This is a model developed by Kielhofner, first published in 1980. It is largely used within the occupational therapy profession. It is a version of the biopsychosocial model of illness and shares almost all the same features. It was developed particularly in relation to occupational therapy, and has a focus on aspects of occupational therapy.

The main features are:

  • the understanding that health comprises a hierarchical series of complex systems
  • the acknowledgement that the environment is of crucial importance, and the environment itself is comprised of hierarchical systems
  • the concept of occupation being an interaction between a person and their environment (similar to activities and participation in the biopsychosocial model)
  • the focus on social roles and the patient having their own purpose in life.

This was an early expansion and development of the original biopsychosocial model. It includes nothing over and above the holistic biopsychosocial theory. It is very similar to the holistic biopsychosocial theory of illness, but probably now less well known.

Psychiatric models.
The biopsychosocial model was developed within the context of psychiatry. There are other models within psychiatry that have been put forward. They include:

  • the biomedical disease theory
  • the ‘content theory’, which focuses on a person’s thoughts
  • behavioural models, which focus on a person’s behaviours
  • psycho-dynamic models, which focus on emotional attachments
  • socio-cultural models, which focus on a person’s social context

All these different psychiatric models are simply focusing on different parts of the overall holistic biopsychosocial theory of illness.

Paediatric models.
Most of these are similar to the biopsychosocial model, taking a systems theory approach with hierarchical levels. The one very important point made in paediatric models, unsurprisingly, is the importance of time, especially as it influences development of the child over time. The ‘temporal context’ has been incorporated into the holistic biopsychosocial theory described on this site. It was absent from the original theory, and is absent from the WHO ICF classification’s model.

Other models.
There are many other models. Many are probably of historic interest only. Many focus on particular patient groups (e.g. learning disability) or professions (e.g. nursing) or other aspects of rehabilitation. Most if not all are simply special instances of the holistic biopsychosocial theory which, like all good theories, has evolved over time as weaknesses (such as the failure to acknowledge the importance of time) became evident.

Criticisms of the theory.

The articles criticising the biopsychosocial model of illness fall into two groups.

The first group are critical of the use made of the theory when making clinical or other decisions about individual patients. They suggest that the model is used to disadvantage people who are ill. They often refer to its use in relation to employment and employability.

It may well be true that individual healthcare professionals misuse the theory, or misinterpret observations in the context of the theory. Nonetheless this does not invalidate the theory any more than the development of an atom bomb invalidated Einstein’s theories. The theory helps analyse a situation. It cannot give a solution or decision.

The second group of criticisms are critical of the analysis of a particular condition using the theory. There are a few patient support groups related to a variety of conditions that criticise the theory.

The grounds for the criticism put forward has two steps. The first is that the theory suggests that factors other that disease should be taken into account when making clinical decisions. The critics often do not agree with this proposal, The primary reason for disagreement is that the critics believe that illness can only have a single cause. They interpret the proposal that many factors can relate to the nature ad severity of an illness to mean that the biopsychosocial theory is denying that disease might be the initial cause of, or contributing to, the condition concerned.

These critics combine an unwillingness to accept that almost all illness has many factors contributing towards the patient’s clinical state with a logical fallacy that having many factors means that disease is not a factor. These critics are wedded to the biomedical theory of illness, denying the influence of other factors.

The biopsychosocial theory of illness cannot itself prove or refute any hypothesis about any illness. It does not carry any implications about cause of illness. It simply provides a systematic framework to allow a full analysis.

In summary, the apparent criticisms do not identify any weaknesses in the theory. One category of criticism is concerned with the use of the theory when making clinical decisions, and possibly be extension when writing policies and protocols. The other category of criticism arises from a misunderstanding of the nature of any theory, and the logic of determining causal relationships. No theory can prove or disprove causation within the framework of the theory; that will depend upon a logical analysis of the available evidence.


My primary conclusions are in this table.

The holistic biopsychosocial model of illness is better considered as a theory of illness
Illness refers to the person’s experience of ill-health; disease refers to a change in the structure or function of part of the person’s body.
The biomedical model of illness is better considered as a theory of disease.
There are many illnesses, and many aspects of illness, that the biomedical theory of disease cannot explain in its guise as a theory of illness.
The holistic biopsychosocial theory of illness predicts and can explain all observations made about illness,
The holistic biopsychosocial model of illness has demonstrated its utility and usefulness in many settings and fields, especially in clinical practice.
There are other theories of illness but they are all either focused on some particular aspect of the holistic biopsychosocial theory of illness, or are very similar.
The criticisms of the biopsychosocial theory (a) relate to its use in making decision or (b) are wedded to a strict biomedical theory of illness, denying the possibility that multiple factors might influence an illness. The critics misunderstand the nature of a theory, believing that it proves or disproves causation which theories cannot do.
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