A psychiatrist has described as "unreliable" the findings of a number of studies which indicate that the welfare of children is not adversely affected through being raised by a lesbian mother or by two lesbian partners.
Such findings could not be relied upon in relation to the long-term development of children because of the methodology used and the small samples involved, Prof Patricia Casey said.
The studies in question were outlined to the High Court last week by experts testifying on behalf of a lesbian couple, Dr Katherine Zappone and Dr Ann Louise Gilligan, who want the State to recognise their marriage in Canada as valid.
Yesterday, Prof Casey, professor of psychiatry at UCD, said she "could not draw any conclusions" from the studies because of certain techniques used and the small sample sizes involved.
More vigorous studies were needed, she said. She was giving evidence on behalf of the State in the action by Dr Zappone, a public policy consultant, and Dr Gilligan, an academic, who in proceedings against the Revenue Commissioners and the State, claim the failure by the authorities here to recognise their Canadian marriage as valid breaches their rights under the Irish Constitution, European Convention on Human Rights and the European Charter of Fundamental Freedoms. They also argue that, if their Canadian marriage is not recognised, they should have the right to marry within the State.
The defendants deny the alleged breaches of rights.
Yesterday, Prof Casey told Mr Donal O'Donnell SC, for the State, that any long-term conclusions from existing studies as to the long-term development of children raised by lesbians could not be relied on because "of the small samples used" and because of the methods used.
The claims about the welfare of children raised in same-sex families, on scientific grounds, could not be supported because nobody knows what the reality is, she said.
Only one of the studies mentioned during the case was a longitudinal one - which pursued children to the age of 25 - and while there had been work done in relation to lesbian couples, no study had ever been carried out about children raised by homosexual men, Prof Casey said.
Also yesterday, Prof Linda Waite, giving evidence from Chicago via video link, said she had carried out a study on the institution of heterosexual marriage which supported the conclusion that heterosexual marriage improves the physical and emotional health of the partners with benefits also accruing to children.