Understanding Life Expectancy at Age One

Life expectancy at age one refers to the average number of additional years a person is expected to live, given that they have already reached their first birthday.

Analyzing the Options

• Option 1: Includes mortality of all the population - Incorrect. This is too general. Life expectancy at age one is specific to individuals who have already survived infancy.
• Option 2: Includes age-specific death rates of all ages - Incorrect. Similar to Option 1, this doesn't account for the specific condition of being one year old. The calculation starts from age one, not from birth covering all ages.
• Option 3: Includes both morbidity and mortality of population on or above age one - Incorrect. Life expectancy primarily measures mortality (death rates). While morbidity (illness) affects healthspan, it's not the direct input for life expectancy calculation.
• Option 4: Excludes the influence of infant mortality - Correct. Life expectancy at age one begins its calculation from the point a person has completed their first year of life. Therefore, the probabilities of dying during the first year (infant mortality) are inherently excluded from this specific measure. It reflects the survival experience of the population *after* infancy.

Conclusion

The key distinction for life expectancy at age one is that it assumes the individual has already survived the risks associated with the first year of life, including infant mortality. Thus, Option 4 accurately describes this characteristic.