The United States ranks 50th out of 224 nations in life expectancy, with an average life span of 78.1 years, according to 2009 estimates from the CIA World Factbook. It can be easily judged that the higher the government expenditure on health care, the higher will be the longevity, as the mortality rate will then be significantly lowered. You may take a look at the old statistics, informing about the life expectancy of the people in ancient times. They are quite shocking. For instance, the average life expectancy in Colonial America was 'less than 25 years' in the Virginia colony. In New England, about 40% of children failed to reach adulthood. The 'Industrial Revolution' was responsible for the dramatic rise in the life expectancy of children worldwide. Public health measures have significantly contributed towards the increased longevity. Studies show that during the 20th century, the average human life span in the United States increased by more than 30 years, of which 25 years can be attributed to advances in public health. Life Expectancy Life expectancy of human beings is defined as "the average age that a group of newborn people would reach, if they are subjected to the age specific death rates in a particular year". Life expectancy is also considered as the expected number of years of life remaining at a given age. Mostly, life expectancy at birth is taken into consideration. Aging is an unavoidable factor of life. The life expectancy of a group of individuals may vary according to the criteria used to select the group. It is usually calculated separately for males and females. According to the CIA World Factbook, Macau has the world's highest life expectancy of 84.4 years. The following table shows average life expectancy of the people in the countries that top the list made by the United Nations (2005-2010) and it also shows the countries that exhibit very low life expectancy. Average Human Life Expectancy

Rank	Country	Overall Life Expectancy at Birth (years)	Life Expectancy at Birth (years): Male	Life Expectancy at Birth (years): Female
1	Japan	82.6	79.0	86.1
2	Hong Kong	82.2	79.4	85.1
3	Iceland	81.8	80.2	83.3
4	Switzerland	81.7	79.0	84.2
5	Australia	81.2	78.9	83.6
191	Lesotho	42.6	42.9	42.3
192	Sierra Lione	42.6	41.0	44.1
193	Zambia	42.4	42.1	42.5
194	Mozambique	42.1	41.7	42.4
195	Swaziland (40% below world average)	39.6	39.8	39.4

It is quite clear that, in countries where individuals pay for their own care, they often don't get treatment until their symptoms become severe. In such countries, there is less emphasis on preventive care. According to the statistics presented by the researchers, a single-payer system seems to be associated with increased longevity. The federal governments of Norway, Sweden, Denmark, Australia and Canada are the payers for the respective health care systems and these countries exhibit some of the highest life expectancies in the world. It has been observed that in the countries where the longevity is lower, infant mortality rates are higher. The infant mortality rate can be taken into account for calculating the average life expectancy but usually, it is difficult to get the exact figures of pre-natal mortality (miscarriage or abortion). Factors Influencing Human Life Expectancy Life expectancy of the human beings is different in different parts of the world because of the differences in public health, medical care and diet. Wars, starvation and spread of the diseases like HIV/AIDS, malaria, etc. are responsible for much of the excess mortality in poorer nations. Climate, economic circumstances, gender also have an effect on human life span and the way data is collected may also influence the figures. Life expectancy is significantly affected by exposure to high levels of air and water pollution. It is a fact that well-educated professionals working in offices have a high longevity, while coal miners (and in prior generations, asbestos cutters) do not. Other factors affecting the longevity are genetic disorders, mental illnesses, physical illnesses, obesity, stress, access to health care, diet, exercise, tobacco smoking, drug use and excessive alcohol use. Life expectancy is useful in determining the retirement age of the people. The term life expectancy, generally used in the context of human populations, is helpful for the analysis of life tables (also known as actuarial tables) which provide the necessary guidelines to the insurance companies. Increased human life expectancy is considered as a symbol of healthy modern life.