Time

The time frames are different at each level

Change and management at levels of pathology and impairment are generally quick (hours/days), but change and management at levels of activities and participation are generally slow (weeks/months/years)

Systems managing different levels should be separated; people with rehabilitation needs are inappropriately placed in an environment focused on disease management

Health services

Hospitals and health services focus on pathology

Hospitals are environmentally unsupportive of disability; hospital systems are procedurally set in short time frames (hours/days); health service data is usually predicated on a definite diagnosis which is often not available, certainly at presentation

Dependence at the level of disability determines main cost of long-term ill health

Supportive care provided is main resource used in health care, even in acute phase. The resources used are not related reliably to pathological diagnosis.

Payment for services should not be related to diagnosis; they should relate to dependence and to rehabilitation treatments needed.

Disability and context

Disability refers not only to ‘quantity’ (e.g. dependence or otherwise) but also to quality

For some people it matters more how normally they act than whether they can undertake an activity; the social implications of altered behaviour may restrict that behaviour; measures rarely take account of the quality of task performance

Outcome measures should therefore consider the perspective of the person in addition to that of others

Disability is strongly influenced by the goals of the patient (the personal context)

All behaviour is goal-directed, and so disability cannot be considered ‘context free’; many factors including financial considerations may determine the activities undertaken by a patient.

Patient-centred treatment requires a good understanding of the patient’s goals, interests, and concerns

Observed disability also depends upon the physical and social context

How someone behaves is inevitably affected by environmental factors and may be significantly constrained by the environment. The ‘environment’ includes the capabilities, wishes, and expectations of relevant others

Interpretation of outcome requires information about context

Relationship between levels

The nature and extent of the relationships between levels are weak

For example patients may have ‘silent’ pathology (i.e. disease without symptoms or signs). This gives scope for rehabilitation. It also implies that measures of the extent of pathology are poorly related to the extent of disability in many cases

Causal relationships may extend in any direction, ‘up’ or ‘down’ the hierarchy

The relationships are not all one way from pathology through to handicap. Changes in behaviour may ‘cause’ pathology. For example, electively not moving a shoulder may lead to the pathology of adhesive capsulitis (frozen shoulder)

Not all illness need start from pathology

A systems analysis of the model would predict that illness may start at any level, and interact down the systems as well as up the systems. Abnormal beliefs (part of personal context) may cause as much disability as pathology (abnormal organ structure or function)

Psychologically determined illness is common in neurological practice, and this model both predicts it and may help understand and manage it

Prognosis depends upon pathology (if present)

The prognostic field for an individual patient is usually determined by the specific disease, but the specific prognosis within that field for a particular patient is usually related to impairments and other factors

Measures should only encompass items from one level

It is invalid to add scores from items or measures covering domains from different levels

Measurement and normality

‘Normal’ becomes much less easy to define, and becomes increasingly personal

Pathology

Structure or function measured against any human, with some allowance for age and gender

Impairment

Structure or function measured against humans matched for age, gender, and other demographic characteristics.

Activities

Behavioural performance and repertoire measured against:

Observation

Comment

Participation

Social role performance and social position measured against:

Miscellaneous

The terminology used all assumes abnormality

There are currently no good words for the opposite of impairment, disability, or handicap.

The ‘new’ terminology of limitations on activities and participation overcomes some of this, though there is still no obvious opposite to impairment.

Interventions may occur at many points

While removal of the prime cause of an illness is the ideal, and this prime cause will often be at the level of pathology, interventions at other points are often also effective, especially when there is no pathology or when pathology cannot be altered