Life expectancy

Question

What is the life expectancy of a girl born in 1994?

Answer

Hello,
The answer to your question, however clearly stated, is not simple.
Life expectancy is, by definition, the average number of years a group of people can expect to live in conditions of mortality determined. But it should be distinguished:
• First, the life expectancy of a generation that is to say, a population of individuals born in a given year,
• On the other hand, life expectancy at a given time in a population of individuals living regardless of their year of birth.
The life expectancy of a generation is calculated by averaging the ages at death of all individuals born in the year of the generation in question. To calculate it, we must expect that all individuals of this generation have died. For example, in France, the 1900 generation lived an average of 52 years (48 years for men and 56 years for women). The indicator depends on the sanitary conditions that people have known throughout their lives, in the example, throughout the twentieth century. It will have to wait probably 2100 or beyond, to calculate the life expectancy of the general French population born in 1994 and almost as long to calculate that of patients with cystic fibrosis born in the same year (note that at the time of the 2011 survey of the French Cystic Fibrosis Registry, the oldest patient was 87 years old).
Life expectancy is calculated from the time when we want to characterize the health conditions of a given year. To do this, we calculate the average age at death of a synthetic cohort of newborns who would be subject to mortality ratio observed at the time of the study for each age (number of deaths divided by the number of individuals in each age group). So, taking the example of the general population in France in 1900, life expectancy at birth was 45 years (43 years for men and 47 years for women); in 2000, it was 79 years (75 years for men and 83 years for women)! This example of the general population illustrates that this value should be interpreted and projected to the future with great care. The life expectancy at a given time can, in fact, remain stable over time if mortality conditions are themselves stable over time. This is absolutely not the case in the general population and it is even less for people with cystic fibrosis (especially with the development prospects of therapeutic molecules involved in the cellular mechanism of the disease).
Precisely because of misunderstandings in the interpretation of life expectancy at a given time, this value is not calculated in the French registry of cystic fibrosis. It is replaced by a curve called Kaplan-Meier survival that gives real patient cohorts according to their year of birth since 1992, date of creation of the French registry (see Report 2011, page 11: www.registredelamuco.org).
These curves represent the evolution of populations of patients and should be interpreted with caution since we want to represent the evolution of a given individual. The evolution of the disease depends on many factors individual genetic (influence of genotype and gene called "modifiers") but also environmental factors (influence of a lifestyle more or less healthy, exposure to factors toxic, allergic or infectious ...).
These factors make individual singular and unique the course of each patient.
Hope that answers your question.
Dr Gilles RAULT in cooperation with M. Gil BELLIS (Institut national d’études démographiques)

05.03.2013