Median survival age
Everyone says that median survival age in Québec is 53 years. I have also heard the expression “life expectancy.” Would you explain these two expressions?
The expressions “life expectancy” and “median survival” are often used interchangeably because they both represent the estimated mean value of life span. However, the two numbers are obtained by different calculations, and median survival is the better indicator with regard to cystic fibrosis.
Life expectancy refers to average life span. To obtain that number, it is necessary to have a good idea of the longest probable life spans in a given population. Consequently, life expectancy is often calculated for large, stable populations, such as the population of Canada, or for disease groups in which the survival time from time of diagnosis to time of death is short. This number cannot be calculated for the cystic fibrosis population because survival time is increasing and we do not know what the ceiling is.
Median survival specifies the age beyond which 50% of the population in question can expect to survive. This calculation requires no prior knowledge or speculation about the longest survival time. Median survival in cystic fibrosis is based on current death rates calculated for each year of age. In 2017, the current median survival age of people with cystic fibrosis is 53 years. If the death rate continues to decrease, this figure will become an underestimation of future survival.
I would like to stress that neither life expectancy nor median survival refer to an upper or maximum limit, but rather to an estimated average age of survival.