Biomedical subjects
D J Deeg
Publications and source records attributed to D J Deeg.
[Multidisciplinary study and social conditions--report of discussions in Session 1].
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The association between change in cognitive function and longevity in Dutch elderly.
The association between rate of change in cognitive function and longevity was investigated with data from the Dutch Longitudinal Study Among the Elderly. A group of 211 Dutch persons aged 65-84 years at baseline (1955-1957) was reexamined twice during an 8-year follow-up period, after which mortality was ascertained through 1983. Cognitive function was assessed based on an adaptation of the Wechsler Memory Scale. Rate of change in cognitive function during the 8 years of follow-up was determined by regression on time for each individual. Cognitive function declined significantly over the 8-year period (mean yearly change, -0.28 units; 95% confidence interval -0.34 to -0.22). The rate of decline in cognitive function was strongly associated with subsequent survival time in the ages 70 years and over, with those with a large decline having a short survival time. No association could be demonstrated in the age group 65-69 years. Adjustment for potential confounders did not affect the magnitude of the association. These findings suggest that the rate of decline of cognitive function is an independent predictor of longevity in older persons.
Medical and social predictors of longevity in the elderly: total predictive value and interdependence.
In the Dutch Longitudinal Study among the Elderly, a probability sample of 3149 persons from the population of the Netherlands, initial ages 65-99 years, was followed from 1955 for 28 years. Vital status was determined in 1983 for 84% of the original sample. Multivariate regression models were used to predict the realized probability of dying (RPD), a measure of longevity based on actual survival time, sex and age at baseline. Predictor variables included physical, mental and social indicators of health status. The total variance explained was 20.2%. Objective health (rated by the examining physician) showed the strongest relationship with the RPD. Upon removing objective health from the model, 19.5% of the variance remained explained. Separate analyses were performed for (1) bio-medical, physical and mental examination variables, (2) disability and health care use variables, and (3) social and psychological variables; in each case the variance explained was over 11%, demonstrating considerable interdependence among predictors. Across different regression models, bio-medical and disability variables proved to be the most stable predictors of longevity.
A measure of survival time for long-term follow-up studies of the elderly.
Studies of determinants of longevity in the elderly by means of a follow-up study are usually based on samples with a wide age range and some selectivity. This poses the problem of constructing a measure of longevity that: (1) will make subjects in the sample comparable regarding survival time, independent of their age and sex; (2) is suitable for long-term follow-up studies; (3) can be used to check the absence or presence of selectivity of the sample with regard to longevity; (4) improves the comparability of studies with different designs and sampling schemes; (5) can take the mortality development over time into account. An individual measure of survival time is presented that satisfies these requirements: the realized probability of dying (RPD). Its construction is described. The RPD is derived from population life tables based on age, year of birth, and sex. For each subject, the relative position on the survival curve within the birth cohort is determined. In an illustration, the RPD is applied to data from a 28-year follow-up study of the elderly in the Netherlands. A comparison is made with other survival measures commonly used in this type of study. It is concluded that the RPD is a powerful and valid measure of longevity in elderly subjects, and that it can be useful in the study of determinants of longevity.