With the number of carers for frail elderly people set to fall steeply, researchers in this week's BMJ propose a way to help plan for the deficit.
Many people fear that population ageing will generate a demand for long term care that will outpace the supply of formal care. So to anticipate the future long term care needs of the oldest people, researchers in Switzerland suggest introducing the "oldest old support ratio."
Their ratio is based on four age groups - the young, those of working age, younger retired people (aged 50-74), and the oldest people (aged 85 and over) - and provides information on the number of people potentially available to care for one person aged 85 or over.
Based on current trends, they estimate that the young retired generation will have to play a greater caring role in the future.
They illustrate this by using trends in Switzerland and the United States. For example in Switzerland, the oldest old support ratio has fallen from 139.7 in 1890 to 13.4 in 2003 and the same trend applies in the US. These ratios are expected to decrease to 3.5 in Switzerland and 4.1 in the United States by 2050.
These forecasts highlight the large fall in the potential pool of informal carers, say the authors. And they warn that failure to anticipate the consequences of these expected trends today will be a mistake that will be heavily paid for tomorrow.
The use of this new ratio should help make governments realise the implications of the substantial intergenerational changes that are occurring and aid policy makers to formulate adequate policies, they conclude.
"We need to face up to the huge cost of care in both the formal and informal sector," add experts in an accompanying editorial.
In England it is estimated that 8.5 million people provided informal care in 2000, 3.4 million of whom cared for people over 65 years. Informal care is often unseen and unmeasured and usually falls to families, but as the retirement age increases and families become increasingly fragmented, we do not know if they will be around to help, or indeed, will be willing to help. And with the crisis in pensions, there will be less money for people to buy additional care.
"First world countries have swapped infant mortality and childhood illness for the burden of care of the elderly," they write. "Caring for the oldest old is the price of affluence."