However, life expectancy is not the same as mean, or average lifespan. Rather, life expectancy constitutes the expected number of years, on average, that a particular cohort of individuals in the population will survive if the rate of mortality remains constant (until the maximum lifespan is reached).[2] Life expectancy is thus the median number of years, at birth, that a population born in a particular year is expected to survive.
Example taken and adapted from Wikipedia: in a stationary population where 51% of people die at the age of 5 and 49% dies at the age of 70, the life expectancy at birth (defined in the sentence immediately before the [2]) is 36 years 10 months, whereas the median lifespan is 5 years. Life expectancy is the “same as mean, or average lifespan” in stationary populations no matter how skewed the distribution of death ages is—the reason why it isn’t in real populations is that mortality rates change with time.
From Part 1:
No, it isn’t.
Downvoted—What is it, then? Just objecting doesn’t provide me any useful information :(
Example taken and adapted from Wikipedia: in a stationary population where 51% of people die at the age of 5 and 49% dies at the age of 70, the life expectancy at birth (defined in the sentence immediately before the [2]) is 36 years 10 months, whereas the median lifespan is 5 years. Life expectancy is the “same as mean, or average lifespan” in stationary populations no matter how skewed the distribution of death ages is—the reason why it isn’t in real populations is that mortality rates change with time.