68	PAOLO MELINDI GHIDI
Fig. 3. Life expectancy at birth 1950-2050 (Elaboration on UN data).
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effects of population ageing in the developed countries. Several works have estimated the required level of immigration able to contrast the population ageing. Regarding Europe, the European Commission estimates that in order to stabilize the actual dependency ratio, the annual migration flow should be comprise between 5 and 7 millions people.
According to those trends and projections, the number of elderly will grow very fast in the next decades. The more significant index in order to understand this demographic revolution is the dependency ratio. In the period 1975-1995 it declined due to the entry of the baby boom generation in the labor market. This trend has changed in the last twenty years and in the next 10-15 years the dependency ratio will increase about 18 percen-tage points in the US, 30 in EU and 40 in Italy. At the same time also the elderly' dependency ratio will increase dramatically. For instance, we can observe as in 1985 the ratio between elderly and population in working age was about 20% in Europe; in other words there were 5 potential workers every old. According to the UN estimates, in 2050 there will be only 2 potential workers every old. This trend will be more strong in Italy and Ja-pan, since the 'elderly' dependency ratio will reach percentages respectively about 65% and 70%. In terms of macro-areas the Western Europe will be the area with the greater dependency ratio value.
When population is ageing there is another important aspect that should be considered, because the problem is not only 'how much' population is ageing but also 'how' population is ageing. At the present time the