HOW MEDICAL ADVANCES AND HEALTH INTERVENTIONS WILL SHAPE FUTURE LONGEVITY
Lisanne A Gitsels, Elena Kulinskaya and Nigel R Wright
ABSTRACT
Medicine related research includes numerous studies on the hazards of mortality and what risk factors are associated
with these hazards, such as diseases and treatments. These hazards are estimated in a sample of people and
summarised over the observed period. From these observations, inferences can be made about the underlying
population and consequently inform medical guidelines for intervention. New health interventions are usually based
on these estimated hazards obtained from clinical trials. A lengthy lead time would be needed to observe their effect
on population longevity. This paper shows how estimated mortality hazards can be translated to hypothetical
changes in life expectancies at the individual and population levels. For an individual, the relative hazards are
translated into the number of years gained or lost in ‘effective age’, which is the average chronological age with the
same risk profile. This translation from hazard ratio to effective age could be used to explain to individuals the
consequences of various diseases and lifestyle choices and as a result persuade clients in life and health insurance to
pursue a healthier lifestyle. At the population level, a period life expectancy is a weighted average of component life
expectancies associated with the particular risk profiles, with the weights defined by the prevalences of the risk
factor of interest and the uptake of the relevant intervention. Splitting the overall life expectancy into these
components allows to estimate hypothetical changes in life expectancy at the population level at different morbidity
and uptake scenarios. These calculations are illustrated by two examples of medical interventions and their impact
on life expectancy, which are beta blockers in heart attack survivors and blood pressure treatment in hypertensive
patients. The second example also illustrates the dangers of applying the results from clinical trials to much wider
populations.
KEYWORDS
Medical intervention, hazard ratio, chronological age, effective age, life table, life expectancy.