The concept of disability is complex and there is no single
agreed definition which suits all purposes (Altman, 2001; Lawton
and Lawrence, 1994; Murray and Chen, 1992; WHO, 2002). The
presence of difficulties in performing everyday activities is often
used to operationalise the concept of disability where the purpose
is to determine the need for care services. In the US, a substantial
decline among older people with such disability was documented
from the mid-1980s to the late 1990s
despite evidence of increases in chronic conditions