Demand for long-term care is driven by the number of people with disabilities that prevent them from being able to undertake essential daily activities without assistance. For policy makers, knowing likely trends in the extent of this demand is essential for planning purposes. Additionally a greater understanding about trends and differentials in disability and needs for assistance may shed light on potentially modifiable influences on both.

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The extent and severity of disability is an outcome of interactions between chronic disease, person-specific characteristics, such as coping strategies, and environmental influences. The latter include individual-level interventions to slow or modify functional limitation attendant on chronic disease and also environmental factors such as the built environment, housing design, and availability of adaptations and assistive devices. All of these parameters, many of which are potentially modifiable, also influence the interface between disability and need for long-term care.

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An added complexity is that the prevalence of disability is a function of incidence (new occurrence) and duration of the condition and so will be influenced by changes in either of these parameters. Measures such as disability-free life expectancy or proportion of life lived with disability consider this dynamic to the extent that they take into account both disability and mortality. Such measures are also intuitively appealing to policy makers and recognised as important policy indicators. However differences in methods of calculation (e.g. cross sectional versus longitudinal) and the fact that such measures are only as good as the data used to calculate them are not always fully appreciated.

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Currently, there is a large European literature on trends and differentials in disability and in measures derived from them, such as disability-free life expectancy, and a continuing debate about whether or not the proportion of life with disability is being compressed, is in equilibrium or is expanding. Differences between countries or population subgroups in these indicators are potentially valuable as they may help to identify factors which lead to more or less disability at the population level. Such comparisons also need to take account of variations in methods and data sources which may lead to artefactual differences.