A survival curve begins at time 0 with all persons (100%) alive. The curve usually
extends as long as the available data permits.
The graph below has survival curves for two groups: (1) severely disabled
young males who have a life expectancy of about 20 additional years, the blue curve, and (2) the U.S. male
general population with a life expectancy of about 65 additional years, the red curve.
Of the 100% of severely disabled young males alive at age 10, only about 10% are still alive at age 55.
By contrast, in the U.S. male general population, about 90% are still alive at age 55.
The median survival time is the time at which only 50% of the persons
are still alive. Here, the median is 15 additional years (=25-10) for persons like the severely
disabled young male, and 70 additional years (=80-10) for persons in the U.S. male general population.