Models used in the study of the ageing process

A search of the literature has identified a number of models, other than the trajectory of decline, used to define the ageing process and are included in the literature review to increase understanding of ‘trajectory’ and modelling .While the models included in this section are not directly used in this research of the trajectories of decline, it is important to be aware of alternative models articulated in the literature, their theory and resulting conjecture. Also, the trajectory of decline focusses on the end stages of the ageing process, that period preceding death. Thus the trajectory of decline will articulate with these models that describe a framework for understanding the ageing process.

Disability and dependency

In the aged care literature and policy, the word ‘dependency’ is used

interchangeably with ‘disability’. For practical purposes, argues Gibson, they are one and the same. However, Fried warns, disability should not be used

Page 99 of 242 interchangeably with the terms frailty and comorbidity because they require different care and research strategies (Fried L, Ferrucci L et.al. 2004). The classic measures of disability, the ADL and IADL, are in fact measures of dependency in that the measure is the level of assistance needed by the person to shop or bathe (Covinsky K, Hilton J et.al. 2006). Dependency, as measured by the functional status, is the most important predictor of the cost of nursing home care (Williams B, Fries B et.al. 1994).

Another area in ageing where dependency is overtly or covertly created in the aged is financially with expectations of leaving the workforce and the

provision of the aged care pension; and from the perspective of the carer, often a woman, who by taking on the ‘burden’ of care for an elder, also becomes financially vulnerable (Gibson 1998, p201).

There is a risk when focussing on the negative – burden of ageing, tsunami of aged, cost of dependency, to name a few phrases – of forgetting that

approximately one-third of people over 60 years are ‘successful agers’

particularly in regard to an absence of disability (Jeste D, Depp C et.al. 2010). As well, pessimism may limit debate on good aged care vs cost (Coorey M 2004).

Life course approach to modelling the trajectory of a person’s life.

The basis of this concept arose in the early twentieth century when the

importance of a person’s early life, even in utero, affects adult characteristics – biological, psychological, social risk factors as well as age-related disease, functional decline and disability (Leinonen R, Heikkinen E et.al. 2001). At a recent symposium published in the Journal of Gerontology, Alwin described the current state of this concept:

A body of work referred to as the “life course” framework (also known as “life course theory,” the “life course paradigm,” and the “life course perspective”) has been increasingly used to motivate and justify the examination of the relationships among variables in social and behavioral science, particularly in the study of population health and aging. Yet, there is very little agreement on

Page 100 of 242 what some of these concepts mean, and there is hardly any agreement on what the “life course” is (Alwin D 2012).

International Classification of Functioning, Activities and Participation (ICF)

The ICF is the international standard to describe and measure health and disability9 (WHO 2001). This tool is linked to the ICD10. There seems to be only limited implementation of this standard in research of disability in the elderly (Guralnik J and Ferrucci L 2009).

The Disablement Process

In the model proposed by Verbrugge and Jette (1994) the ‘Disablement Process’ (diagram shown in Figure 2.22 was drawn by Avlund 2003 based on the concept of Verbrugge and Jette 1994), identifies domains of measurable change in ageing.

Figure 2.22 From (Avlund K 2003 p316): The Disablement Process

‘Pathology’ in this model, refers to physiological abnormalities that can be detected and measured or medically labelled such as a stroke. ‘Impairments’ are dysfunctions that can be evaluated using clinical examination, such as a

Page 101 of 242 peak flow measure. ‘Functional limitations’ are restrictions on the person’s ability to undertake basic daily physical and mental tasks matched to age group regardless of the context of the function. This contrasts to ‘Disability’ which measures a person’s ability to undertake a specific task. Most common measures of this domain are activities of daily living (ADL) which are either physical – bathing, walking or eating for example; or instrumental activities that a person needs to be able to do to manage living in society – banking, catching a bus or taking medications. The strength of this seemingly simple concept is that the disablement process can turn into a series of feedback loops whereby someone with arthritis may stop walking, develop social isolation and spiral into increasing weakness and frailty (Verbrugge L and Jette A 1994).

‘Successful’ Ageing

Using a British dataset of community living participants, Bowling and Iliffe (Bowling A and Iliffe S 2006) tested five models of ‘successful ageing’ they had derived from the literature. They found that the lay based model predicted quality of life better than the other more one-dimensional measures (Figure 2.23).

Figure 2.23 Five Successful Ageing models from Bowling and Iliffe (2006, p609)

A later review Jeste (Jeste D, Depp C et.al. 2010) identified ten different domains of successful ageing in the quantified research literature the most common being disability/physical function, cognition and then life satisfaction

Page 102 of 242 measures. These authors concede that there is no agreed definition of what comprises ‘successful ageing’.

The compression of morbidity

The concept of ‘compression of morbidity’ has been contentious since its introduction by James Fries, Professor of Medicine at Stanford University in an article in the New England Journal of Medicine in (Fries J 1980). This theory has been contentious (Crimmins E and Beltran-Sanchez H 2010) despite supporting empirical evidence (Vita A, Terry R et.al. 1998).

Life expectancy, as introduced in the previous chapter, is high in Australia. However it must be remembered that as with population predictions, the determinant ‘life expectancy’ is hypothetical. Debate about these hypothetical trends uses the following arguments:

‘compression of morbidity’=the argument that due to improvements, current and future, in health care that morbidity will be ‘compressed’ into an

increasingly shorter period toward the end of life; or,

‘expansion of morbidity’=whereby increasing years of life will be associated with increasing periods of morbidity; or,

‘dynamic equilibrium’=is somewhere in between. While prevalence of disease (level of morbidity in the population) may increase due to increased survival, due to healthcare, the severity and impact of diseases is reduced (Crimmins E and Beltran-Sanchez H 2010; Australian Institute of Health and Welfare 2006).

An example of the use of this concept in predicting demand for health care services by an ageing population is described by Caley and Sidhu (Caley M and Sidhu K 2010) who demonstrated the effect of three different modelling approaches on estimating future costs. The most cost effective model relied on investment of the health system in preventative health measures to ensure a healthy population that live into old age with fewer illnesses – the

Page 103 of 242 morbidity has been in place for heart disease, stroke and cancer for example, but there is no sign of delay in the onset of dementia (Bruen W 2005).