The publication this week of the Central Statistics Office's revised projections of our future population and labour force is an important development. There have been enormous changes in our economy since the previous projections were published in 1995, including in particular a reversal of past emigration trends.
This has hugely important implications for our future population. Moreover, the recovery in our birth rate, which has risen by 12 per cent since 1994, also raises the question of whether the upper limit of future fertility employed in 1995 might have been on the low side.
In 1988, when the first of this series of population projections was published, the scale of net emigration was such that both the alternative projections then put forward foresaw a drop in our population over the 23 years to 2011 - a decline of the order of 2 to 5 per cent.
By 1995 the expert group advising the CSO had come to believe there had been a small net inflow of migrants in the 12 months to March 1992 but that this had been offset by a net outflow in the following three years totalling 22,000.
That belief led to an assumption that net emigration between 1991 and 1996 would average 7,000 a year, but that in the decade from 1996 to 2006 this annual rate of net emigration would fall by amounts that might range from half to four-fifths - and that after 2006, emigration would cease, with no further net movement in either direction.
(In fact, the trend of migration between 1991 and 1995 had been much more favourable than was thought at the time the 1995 projections were prepared. Over these four years, there had in reality been no net outflow, and we now know that since early 1995, there has been a rapidly rising net inflow of immigrants.)
The outcome of this 1995 revision was a series of alternative projections which ranged from the population remaining almost static - on an assumption involving the higher of the two projected levels of net emigration between 1996 and 2006 as well as a sharply reduced level of fertility - to the population increasing to over 4,000,000 in the 2020s.
This latter projection was based on an assumption that involved a lower level of emigration in the 1996-2006 period, and a more modest decline in fertility.
The current projection, prepared after a period of substantial net immigration, assumes that this recent inflow will persist, albeit at diminishing rates, at least until the latter part of the next decade, and that in the two following decades the population flows will lie somewhere between a 5,000 annual inflow and a 5,000 annual outflow.
In combination with alternative low and high fertility rates, these migration assumptions yield new projections involving population increases between now and the year 2021 that would bring our population up from its present level of about 3,750,000 to between 4,040,000 and 4,560,000. After that it might either fall by something less than 10,000 a year or rise by as much as 20,000 a year - depending on the migration assumption used for the 2020s.
What is new about this is that a population in excess of 4,000,000 in 2021 is now seen as the most pessimistic rather than the most optimistic outcome, and an increase to over 4,500,000 is now seen as possible, if perhaps unlikely.
The Expert Group that has assisted the CSO with this exercise and the previous one is drawn from a range of Government departments and from the ESRI and several higher education institutions. It is the belief of this group that the recovery in fertility between 1994 and 1998 may reflect a "once off" postponement effect, as women in their 30s have been having babies who at an earlier time would have been born when their mothers were in their 20s.
The group believes this temporary boost to the birth rate is likely to be offset in the longer run by the rising participation of women in paid employment and by increased educational attainment among women - for education increases employment prospects and has a negative effect on the marriage rate.
Moreover, despite the steep fall in fertility during recent decades, fertility rates here are still a good deal higher than elsewhere in Europe - and in the rest of the continent these rates are still declining. Clearly the group expects fertility to move towards the lower end of their range of assumptions.
On this basis, even if the group's more favourable immigration assumption proves justified, our population in 2021 would be unlikely to exceed 4,300,000 - 4,450,000.
How realistic are the group's projections for migration? Its assumption that net immigration will continue at least until 2006, and possibly on a reduced scale during the quarter of a century thereafter, reflects an expectation that our economy will remain buoyant, thus giving rise to an increased demand for labour which we will have difficulty in supplying exclusively from domestic sources.
But the external "pull" factors drawing some Irish young people to employment elsewhere are more difficult to assess.
On the one hand, if there were a downturn in the economies of some of the countries to which emigrants go, this could increase the flow of emigrants returning here. But if that did not happen, the ageing population structure of other European countries could in time draw more of our young people away.
The expert group does not refer to the possibility, which has been canvassed elsewhere, that the high cost of housing here might depress the inflow of immigrants - about half of whom are not in fact returning Irish emigrants but foreign nationals coming here for work, and some of whom are spouses of returning Irish emigrants.
While the high cost of accommodation could affect the flow of immigrants in the short term, the housing problem will rectify itself in time, as supply catches up on demand, halting the increase in, or perhaps even reducing, house prices.
One cannot exclude the possibility that because of the imminent tapering-off of the increase in our labour force, the level of net immigration may in fact turn out to be higher during much of the first quarter of the next century than is implied even by the more optimistic of the group's two alternative emigration scenarios.
These projections also include estimates of our future labour force, but because of uncertainties about labour force participation rates in the longer term, these are limited to the period up to 2011.
Depending on the migration assumption employed, these latter projections yield alternative labour force figures for 2011 in the 1,900,000 to 1,985,000 range. This compares with 1,650,000 at the start of this year. The increase in the male labour force over this 12-year period is estimated at 9 to 13 per cent. For women, it is estimated at 25 to 30 per cent.
Assuming a 5 per cent unemployment rate in 2011 - a figure that we are likely to attain next year - this suggests that 12 years from now our dependency ratio, (the proportion of dependants to people at work) will have fallen to between 1.13 and 1.25. This would be half the figure that applied in 1986 - 2.29 - a ratio that was then 50 per cent above that of the rest of the EU.
By early this year our dependency rate had fallen to 1.40, now fractionally lower than the EU average.
This dependency ratio is a crucially important factor influencing living standards. In fact, as much as half of the catching-up of average Irish living standards vis-a-vis those of the EU that occurred during the 1986-1996 decade was accounted for by the drop in the dependency ratio - the other half being the consequence of the faster rise of labour productivity in Ireland.
Because the further fall of between 10 and 20 per cent in our dependency ratio to which we can look forward over the next dozen years is unlikely to be paralleled in the rest of the EU, we are likely to continue to catch up on our partners' living standards even faster than would be accounted for simply by a more rapid rise in labour productivity in Ireland.
The number of children and young people who will require to be educated during the early decades of the next century naturally depends largely on our birth rate - although our educational numbers will also continue to be influenced to some degree by the level of immigration. Throughout this decade, immigrating adults have been bringing with them an average of almost 6,000 children a year, which has been adding about one-eighth to the number of children born here each year.
On the basis of the more optimistic of the group's two migration assumptions, combined with the middle-of-the-road fertility assumption, the number of children under 14 would bottom out about the year 2001 at just over 825,000 - down by almost a quarter from the peak 1,025,000 of 1986.
During the first decade of the next century this number would rise to about 875,000, declining again, however, from about 2015 onwards. No doubt these new projections will in their turn need to be revised in a few years in the light of developments in infertility and migration in the intervening period.
It seems unlikely, however, that such a revision will need to be anything like as drastic as the one published this week, which has had to take on board all the consequences of the recent reversal of traditional Irish emigration.