Health, quality of life and individual life-trajectories

Longitudinal studies of health and quality of life have become widely available. However, much of the analyses do not fully explore the advantage of individual life trajectories. During the last two decades a handful of studies analyzed courses of health and disability by exploring individual-level trajectories of functional impairment and disability. We present two examples, where the study of individual life trajectories brings new insights.
The first example is the cross-national comparison of the health status of populations. Past studies of health differences between countries mainly focused on the level of health calculating e.g. healthy life years. The comparison of health levels, however, is biased e.g. by cultural differences in answering health questions even when the same question is used in international surveys such as the ECHP. We present the results from two panel studies, the German Socioeconomic Panel and the Hungarian Household Panel to study individual health trajectories for 3825 individuals who survived the period 1992 to 1997. Rather than on focusing on the level of health we explore the slope of the health trajectories. A cluster analysis identifies four distinct trajectories - (1) decline, recovery, (2) stable, (3) early decline, (4) late decline. The frequency of these four trajectories differs significantly between the two parts of Germany and Hungary: Hungarians are less likely to follow stable health trajectories and are twice as likely to experience an early decline in their health. This discrepancy is independent from the differences in the age and sex distribution of the two countries.
The second example deals with age-specific trends in the quality of life. Past studies have repeatedly pointed out the paradox of stable subjective well being despite severe loss. This paradox, however, is mainly based on cross-sectional studies. A recent longitudinal analysis starts to question the paradox and finds small age-related decline in mean levels of life-satisfaction that seem to accelerate with age. We analyse individual trajectories of subjective life satisfaction in the German Socio-economic Panel between 1995 and 2001 and explore their correlation with trajectories of health. Results show that the age paradox in life satisfaction does not exist. While the level of life satisfaction only changes marginally with age the slope becomes more negative. Corrected for disability and loss of partner the level of life satisfaction tends to increase with age, the slope, however, becomes more negative.