Age trajectories of independence in daily living among the oldest old in China

Abstract

With the rapid increase in the population of the oldest old (those aged 80 and over), there is some concern how longer life might be associated with a loss of independence in daily living. Addressing the trajectory of loss of independence for the oldest old is challenging, not only because the oldest old are heterogeneous, but also because the health trajectories at the population level may noticeably differ from those at the individual level. We used the 1998, 2000, 2002, 2005 and 2008 waves of the Chinese Longitudinal Healthy Longevity Study to assess the age trajectories of the loss of independence for three cohorts born in 1909–1918, 1899–1908 and 1893–1898, respectively, both at the individual and the population levels. Independence was measured by combining the activities of daily living and the Chinese version of the mini-mental state examination. Controlling for various confounding factors, particularly the selectivity due to death and loss to follow-up, we found that, while more recent cohorts had higher initial levels of independence, this was followed by a faster decline compared to the earlier cohorts. Also, their level of independence fell below that of their earlier born counterparts at the same ages. Decomposition analysis further illustrated that the decline of independence at the population level is more gradual than that at the individual level. This finding can be largely attributed to selective mortality and loss to follow-up. For instance, the population prevalence of independence for the 1893–1898 female cohort declined slightly, from 19.7 to 11.1% in 1998–2008, while the proportion for females who survived from 1998 to 2008 dropped from 66.7 to 11.1%. For the population as a whole, a longer life expectancy does not necessarily result in a rapid decline of independence. For individuals, longer life expectancy accompanies deterioration of independence.

Appendices

Appendices

Appendix 1

See Table 4.

Table 4 Distribution of the subjects by sex and place of residence for the final sample (N = 7955) and non-respondents (N = 850) across three cohorts. Total sample N = 8805

Appendix 2

We used data from the sixth wave of the Australian Longitudinal Study of Aging (ALSA) conducted in 1990–2000 to look for the cutoff point for non-cognitive impairment in the MMSE scores. The study sample of the ALSA was persons 70 years old and over and the total sample size was 791. After we excluded the subsample of those younger than 80 and those cases with missing values on the MMSE, the final sample size was 456. The cutoff of 17 for the Chinese version of MMSE may produce the similar distribution of cognition to what the cutoff of 23 for standard version of MMSE does (please see the following table).

Distribution of cognition by different cutoff for standard and Chinese version of MMSE, using the data from the sixth wave of the Australian Longitudinal Study of Aging.

	Freq.	%
Standard MMSE
MMSE < 23	67	14.69
MMSE ≥ 23	389	85.31
Total	456	100.00
Chinese version of MMSE
MMSE < 17	73	16.01
MMSE ≥ 17	383	83.99
Total	456	100.00
Chinese version of MMSE
MMSE < 16	58	12.72
MMSE ≥ 16	398	87.28
Total	456	100.00