A Decomposition of Life Expectancy Levels and Trends

John Bongaarts, Population Council

Life expectancy at birth has risen in the past due to declines in juvenile, background and senescent mortality. To interpret past trends a new procedure for decomposing life expectancy is proposed. This decomposition divides the level of life expectancy at a given point in time into three components which quantify the roles of juvenile, background and senescent mortality. The procedure is applied to historical data from 16 high income countries for all available years, separately for females and males. The observed large increases in conventional life expectancy before 1950 are found to be primarily attributable to reductions in juvenile and background mortality. After 1950 the rate of improvement in life expectancy slowed because declines in juvenile and background mortality slowed, but senescent mortality declined more rapidly than before, thus becoming the main cause of rising life expectancy at birth. The role of smoking in the past half century is also quantified.