The expectation of life
The expectation of life at birth (e0) is often quoted in reports and is a useful and informative measure. However it is also a widely misunderstood measure and this misunderstanding will be dealt with over the next few pages.
The e column allows us to read off life expectancy from any age onwards.
Note that although the expectation of life reduces with age the expected age at death, that is the addition of the attained age and the further expectation of life, increases. The reason for this is as follows. As each birthday is passed you become a member of a smaller and smaller selected group of people who are "survivors". They have survived certain critical periods of risk - most notably childhood with its many childhood diseases and risks of accidents - but also risks associated with growing up such as road traffic accidents, occupational hazards etc. and for women the risks of childbirth. Along the way the survivors have gained advantages in terms of disease immunity, experience of avoiding hazards such as crossing the road, drowning etc. In general they have learnt both consciously and physiologically to resist hazards which others have succumbed to. They may also have been more genetically or physiologically "robust" from birth, although this is usually unknown, and debatable.
It is therefore quite reasonable that a man who at birth had a life expectancy of say 70 years has an expectancy of say a further 60 years at age 20 - because he has already survived 20 years of hazard, much of which (certainly in the case of childhood diseases and learning to cope with traffic) is now behind him. At age 50 he may then have a further expectancy of 35 years - a further increase.
This point is not well understood by lay people. To a lay person the statement that "life expectancy in England in 1600 was only 42" is often understood to mean that people started weakening in their late 30's and were usually dead by 42 - and there were consequently few people walking around much over 42. This is patently untrue, but widely believed.
Part of this misunderstanding is because the figure often quoted as "life expectancy" is actually "life expectancy at birth" but the distinction is not appreciated. That figure is then considered a static figure which applies throughout life, whereas it is actually a very malleable figure which changes as life progresses. The ex column demonstrates this.