For Parents, Caregivers, Treating Physicians, and Patients
We are often asked to provide a life expectancy for a given individual.
To properly give a customized life expectancy requires much detailed
information about the person and an investment of several hours on our part. We regret
that we are unable to do so at this time. For rough approximations, see the appropriate
study on the articles page.
It is important to understand the difference between survival time and life expectancy.
Survival time is the actual time from the present moment until death, whereas life
expectancy is the average (or arithmetic mean) survival time. Some persons will
live shorter than the life expectancy, others may live longer.
For example, if hypothetically the survival times for 5 year-olds with cerebral palsy
are equally likely to be 10, 20, or 90 years, then the life expectancy is (10+20+90)/3=40 years.
It is thus clear that the child will not live exactly 40 more
years -- the child could only live shorter (10 or 20) or longer (90). In an actual case, the
possible survival times may vary from 0 to 100 additional years, but the principle would remain:
life expectancy is not a prediction about actual survival time.
The above is equally true, of course, for the
general population. In the United States, a female
aged 30 has a life expectancy of approximately 50 years. This is not to say that she will live an
additional 50 years -- because she could live to age 100 or (tragically) die tomorrow in
an auto accident. What is true, however, is that the average survival time of
women aged 30 in the U.S. is 50 additional years. It is important to keep this distinction in mind
when reading any literature on life expectancy.