最後一夜 (唱: 蔡琴)
technical note 88
30-year mean rainfall in Hong Kong 1961-1990
M.C. Ng & K.P. Wong
(From Roman Empire, OUP VSI, p.104-105)
The `model life table' most commonly applied to the Roman empire is conventionally known as `Model West, level 3'. It assumes both a stationary population (that is, with a zero growth rate and a constant age structure) and one stable over time (that is, without the effects of either migration or plague). The two columns on the left in Figure 19 track a notional cohort of 100,000 females at five-year intervals from birth to age 85. The third column gives the average remaining life expectancy at those same five-year intervals. The fourth column gives the percentage of the population in each age group.
Fig. 19: Model Life Table, West level 3, Female
[C] 100,000 Cohort
[E] Remaining Life Expectancy
[%] % in Age Group
The patterns are striking. On this model, only half of all babies survive to age 5; the mortality rate is highest in the months immediately after birth, with about one-third of newborns dying before their first birthday. Those who survive to age 5 have, on average, a good prospect of living another 40 years. Such high mortality results in a young population. The average age in Model West, level 3 is 27.3 years for females and 26.2 for males; or, put another way, just over 40% of the population are less than 20, only 4% are 65 years or older. In crude terms, in Roman society the young generally outnumbered the old by somewhere around ten to one; in sharp contrast, this ratio in modern, Westernized societies is under three to one.
There is a plausible match between this demographic model for the Roman world and the best surviving evidence. It is reasonable to assume that the differing ecological conditions around the Mediterranean (arid land, marshes, mountains, plains) would have had an impact on the life expectancy of their particular populations.