令人感到惊奇的是,在有记载的历史上,所有预期寿命方面的增加有半数是发生在本世纪内,并且大多数出现在本世纪采用现代新药和接种疫苗之前的上半叶。例如,美国的预期寿命已由1900年的47岁增加到1995年的78岁。分析不同的国家在本世纪内伴随着人均收入的改变而发生的预期寿命的改变是很有意义的事情。除了全球的预期寿命明显地增高之外,另外还有两点值得提及: Surprisingly, in the documented history, half of all life expectancy increases occurred in this century, and most occurred in the first half of the century before the introduction of modern new drugs and vaccinations in this century. For example, life expectancy in the United States has risen from 47 years in 1900 to 78 years in 1995. It is interesting to analyze the changes in life expectancy that different countries experience with per capita income changes over the course of this century. In addition to the marked increase in life expectancy globally, there are two other points worth mentioning: