On the Accuracy of Life Expectancy

Nan Li, United Nations
Shripad Tuljapurkar, Stanford University

Publishing annual life expectancy by sex to two decimals has become almost customary for countries with reliable death registration, and perhaps a target for other nations. The basis of this standard requires investigation. Following common practice in statistics, we define accuracy as the 95% confidence interval, and provide a simple method to compute the accuracy of calculations of life expectancy. We show that the accuracy of life expectancy is mainly determined by the level of mortality and the size of population. We indicate that, even if death registration and population count were perfect, the accuracy of life expectancy would not reach a year for 30% of all countries, 0.1 years for 63% of all countries, and 0.01 years for any country, even China or India.