The Effect of Increased Longevity on Capital Accumulation
分析美国1970年代寿命延长对储蓄率的影响，基于生命周期模型预测储蓄应上升，但实际数据却显示下降，探讨了可能的原因。
One of the more startling demographic trends of the 1970's has been the sharp rise in lifespan in the United States. Between 1970 and 1980, the life expectancy of 25year-old men and women increased by at least two years. While longevity has been steadily rising for many decades, the recent spurt has hastened the trend; the increase for both men and women in the 1970's more than doubled the improvement of the 1960's.1 The 1970's were also characterized by a decline in labor force participation of older workers. Although rising income and increased disability payments may have explained some of the decline (Donald Parsons, 1980), it seems clear that expanding longevity has not been strongly associated with deferred retirement (Daniel Hamermesh, 1984).2 Thus the retirement years have assumed greater importance in financial planning for the consumer as he or she retires earlier and lives longer. The traditional life cycle model would predict greater savings rates as consumers increase accumulation of assets for their retirement. Consumption while young would drop, and there might be an increase in labor supply as individuals substitute leisure while young for greater levels of life cycle consumption. Even under a Social Security system, as long as the current generation's tax liabilities reflect their longer lifespan, total savings (private plus public) should also rise.3 The predicted increase in savings is substantial. A simple example using the Modigliani-Ando-Brumberg life cycle model can illustrate the extent of the savings shift. Assume that earnings and consumption are constant over working years and lifespan, respectively, and that the interest rate is zero. Consumption is then a constant proportion k of earnings, where k is the ratio of working years to one's lifespan. If consumers made plans based on average lifespan, the representative 25-year-old would have saved 18 percent of earnings in 1970 (1-40/49 when he plans to retire at age 65 and expects to live until age 74). In 1980, after a rise in life expectancy of two years, the representative 25-year-old would have increased savings to 21 percent of earnings, or a net rise in the savings rate (per worker) of 17 percent. That is, this simple life cycle model implies that savings in the last decade should have risen (other things held constant) by approximately 17 percent, or about 80 billion dollars per year. The evidence from aggregate time-series data appears to contradict the life cycle model's prediction of rising savings rates. The net private savings rate in the United States declined from 7.8 percent of NNP in 1970 to 6.2 percent in 1980. While Alan Auerbach (1982) has suggested that some of the reported decline in savings may be caused by mismeasurement, it seems clear that there has been no substantial rise in the savings rate. There are numerous explanations for *Department of Economics, University of Virginia, Charlottesville, VA 22901. I am grateful to Maxim Engers, Daniel Hamermesh, William R. Johnson, Laurence J. Kotlikoff, John Strauss, and especially James Davies and John R. Wolfe for helpful suggestions and comments. 'Life table data can be found in Daniel Hamermesh (1985), the Life Insurance Fact Book (various years), or in unpublished form from the National Center for Health Statistics. 2John Wolfe (1983) provides an ingenious argument for why the Social Security benefit schedule has induced those with shorter life expectancies to retire early. We might therefore expect some rise in the average retirement age as those expecting to live longer defer retirement until age 65. 3If the Social Security taxes do not rise as expected lifespan increases (perhaps because current tax proceeds are paid out as current benefits, rather than retained in a trust fund), young workers will save more to offset the lower expected benefits in the future. 4In a two-period model, the percentage change in savings by the young is equal to the percentage change in aggregate savings.