In the unfortunate absence of the kind of surveys needed to provide a basis for policy decisions on family formation issues, the recently published ESRI Report on Family Formation draws together such information as is currently available on this subject.
Much of this information, on such matters as changes in fertility, the growth and pattern of lone parenthood, and changes in household and family size, will be new to most people. However, I think that almost everyone is aware that one-third of births in Ireland are now non-marital. Indeed, taking account of abortions, just over half of all first pregnancies are non-marital.
But, of course, many one-parent families come into existence for reasons other than non-marital pregnancies - a minority through widowhood, and many more today because of marriage breakdown. One out of seven of all parents with children under 15 was a lone parent in 1997, and the proportion is certainly higher today - perhaps one in six.
In 1996, 6.5 per cent of all married people were separated, or in a minority of cases divorced, but today that figure may be approaching 10 per cent. And, although in 1997, social welfare statistics recorded more unmarried lone parents than separated parents, this may not in fact reflect the true position.
The 1996 census and data drawn from the Labour Force Survey a year later suggest that the number of separated parents with children under 15 is in fact somewhat greater than the number of unmarried parents with such children.
Moreover, it seems likely that only a minority of parents of non-marital children are in fact lone parents. Of the non-marital children born between 1993 and 1996, only two-fifths were living with unmarried lone parents in 1997.
Three-fifths of these mothers had either been cohabiting before the birth of their child, or entered cohabitation or marriage subsequently - although not necessarily with the other parent in all cases.
And as other sources suggest that the proportion of lone parents entering partnerships each year is only between 3 per cent and 5 per cent, it thus seems that a high proportion of unmarried parents must have been in some kind of relationship at the time of the birth of their child.
In fact in a survey of 2,000 pregnant women carried out in 1996 which found that 35 per cent were unmarried, less than one-tenth of these unmarried mothers described themselves as single. The remainder reported either that they were cohabiting (one-fifth) or "going steady" or "engaged" (one quarter each).
While in some respects this is encouraging - the proportion of genuinely "lone" unmarried parents seems to be quite small - studies elsewhere suggest that the relationship breakdown rate in such cases is relatively high.
Thus in the US a decade ago the proportion of cohabitants who remained together after 10 years was only half that for married couples who had not cohabited before marriage.
And at about the same time in Britain the proportion of cohabitants who were still together five years after the birth of their first child was once again half the proportion of married couples.
Clearly, from the point of view of the rearing of children in two-parent families for the sake of the children, marriage has a marked advantage over co-habitation, and the State therefore has a clear interest in encouraging marriage in the interest of social stability.
This report provides for the first time information on the social pattern of non-marital parentage.
For some reason the data in the report are not presented in such a way as to show the proportion of women with different levels of education who are single unmarried mothers, but it is possible to derive this information from these data.
It emerges that levels of education dramatically influence the proportion of non-marital births.
Thus, after excluding the 10,000 married women aged 20-24 who in 1997 were without children, only 1.5 per cent of the remaining 20-24 year-olds with a university education were single unmarried mothers.
But that figure rose to 5.5 per cent for those whose education ended with a Leaving Certificate - and, phenomenally, to 20 per cent for those who left school with an Intermediate or Group Certificate only.
And of those without even an Intermediate Certificate, an astonishing 27 per cent were unmarried mothers.
Clearly, remaining at school until the Leaving Certificate is a hugely important factor in limiting unmarried motherhood: early school-leavers are extremely vulnerable in this respect.
Data for the 35-39 age group in 1997 - those who left school in the 1970s, before sexual mores had significantly changed - show a less emphatic educational differential in relation to unmarried motherhood, but even with this group the 15 per cent of single women with children under 15 who had not gone to secondary education was about four times as high as in the case of the remainder.
Divergences between those with different levels of education are not confined to unmarried motherhood but are also found in respect of marital parenthood.
First of all, among the 20-24 age group - and again excluding those married but with no children - 35 per cent of women without a Leaving Certificate were married and with a child in 1997 - as against only 11.5 per cent of those with university education.
Now that difference is clearly explicable in terms of the different lengths of the educational process: many graduates had not been long enough in employment to have had time to get married before the age of 25.
But when one looks at the figures for those aged 35-44 in 1997 - and therefore old enough to have had ample time to get married and have children - 21 per cent of those with a university education were still single and without children - almost twice the figure for the rest of the population.
It also emerges from this survey that whilst non-marital pregnancies and births are now at a very high level, this has had the paradoxical effect of reducing the birth rate. For on average unmarried mothers have only 1.6 children, whereas married women have an average of 2.7.
I have to say that until this report drew my attention to this point I had failed to realise that our huge increase in non-marital births was keeping the birth rate down!