The future is uncertain, and so are the future populations. This uncertainty is a fundamental aspect of population dynamics. It is affected by various factors such as socio-economic development, technological advances, and even cultural change. Understanding demographic uncertainty is essential in policy-making based on population projection. In recent decades, various methods have been developed to describe the uncertainty, including probabilistic forecast. However, such methods have not got enough attention in China, where the population tends to be highly uncertain due to rapid demographic transition and social transformation. In this paper, we investigate the uncertainty and its policy implications. Specifically, we focus on three major aspects of China's population:the number of births, particularly in the era of universal two-child policy, the number of total population, and the target population of regional planning. Overlooking or underestimating demographic uncertainty can lead to misleading projection results for policy makers and the public. We are in need of developing methods for China's population projections.

The life expectancy of the older people had increased steadily during 1998-2013 in Shanghai, but their disability-free life expectancy had changed from an increasing trend in 1998-2008 to a decreasing trend in 2008-2013. The period of disability had expanded in 1998-2003, then compressed in 2003-2008, and finally expanded again in 2008-2013 as their lifespan increased. The increase of disability-free life expectancy in 1998-2008 was mainly driven by the decline in mortality while the decline of disability-free life expectancy in 2008-2013 was largely due to an increase of disability rates, which offset the increasing effects of mortality reduction. The social and economic development, the advance of medical technology, and the practice of social security system in Shanghai are the main factors leading to the changes of the disability-free life expectancy. This transition from increase to decrease of disability-free life expectancy of the older people have been consistent with the rapid increase of per capita health expenditure in Shanghai since 2008.

Based on the Chinese Longitudinal Healthy Longevity Study (CLHLS 2002~2011),this study assesses the age trajectories of the loss of independence in daily living for five cohorts aged 65~69,70~79,80~89,90~99 and 100+ at the 2002 survey,respectively,both at the individual and the population level.Results show that the decline of independence at the population level is more gradual than that at the individual level.A decomposition analysis further reveals that the difference in the pace of decline of independence can be largely attributed to selective mortality and loss to follow up.Moreover,such difference varies across cohorts.For the population as a whole,a longer life expectancy does not necessarily result in a rapid decline of independence.For individuals, however, prolonging lifespan tend to be accompanied with deterioration of independence except for the young old.