Life expectancy is defined as the number of additional years of life expected at a specified point in time. Which of the following is a commonly used reference point?

• A. The number of people currently alive in a population
• B. The number of additional years of life expected at a specified point in time
• C. The average age at death in a population
• D. The rate of mortality in a population

Answer: (B)

Life expectancy is about how many more years a person is expected to live from a chosen starting point. In practice, the common reference point is birth, so life expectancy is often reported as longevity from birth. The option that states life expectancy is the number of additional years of life expected at a specified point in time matches this idea directly, because it centers on the remaining years from a chosen starting age. The other choices describe related but different measures: how many people are alive now, the average age at death, or the overall mortality rate, none of which specify the starting point or the forecast of remaining years. So this option best fits the concept of life expectancy.