Application of the opinion rule in family law proceedings

This provision was recently considered in the case of Hertz v Hertz [2025] FedCFamC1F 926 per Gill J. The relevant paragraphs which concerned the determination of whether the opinion rule should be applied are extracted below:

[5]  While a cogent argument could perhaps be raised that many of the parenting cases before Division 1 of the Federal Circuit and Family Court of Australia are exceptional due to the nature of the risk issues that are typically raised in those proceedings, there is a particular factor in this case which sets it even further apart from the usual run of cases in this court. That factor is the proposition advanced in the material that each of the parents poses a significant risk to the children, whether by virtue of a sexual risk alleged to be posed under the care of either the father or the mother, or various developmental risks in particular levelled against the mother. Those potential risks were identified by the single expert to be sufficient to suggest the involvement of the welfare agencies in New South Wales or the Australian Capital Territory in order to ameliorate the potential risks arising from each of the parents. That particular factor is sufficient to render the circumstances here as exceptional within what may generally be regarded as an exceptional cohort of cases.

[6]  In this case the issue of the risks to the safety of the children, whether posed by reason of a sexual risk or a developmental risk, are of critical importance in the proceedings. They are the central matters that have been identified by each of the parties.

[7]  The subject matter of the proceedings relates to parenting arrangements for the parties’ two children and in particular as to questions as to how risk of harm may be ameliorated in respect of the children.

[8]  On the mother’s case that involves no contact taking place with the father in the long-term.

[9]  The probative value of the evidence may be understood in this manner: issues of sexual risk and developmental risk are matters that the assessment of is greatly assisted by appropriate expert evidence. The probative value of the expert evidence can be assessed on the basis that if accepted it may in this instance have a significant impact on the case posed by each of the parties. That is, if its probative value is assessed on the basis that it is accepted in the proceedings it indicates significant risks to the children in the mother’s care. The issue of probative value may also be assessed in another way which is that the nature of the subject matter is such that it calls for expert evidence in order to properly resolve it. That is the nature of the risks posed by either of the parties require for resolution expert evidence. As a category, it may be expected that expert evidence is probative to answer those issues. What will give it weight in the proceedings, or admission, is its capacity to do so.

[…]

[11]  Given that what will give expert evidence its cogency in this case is the fact that the specialised knowledge of the single expert, or another appointed expert, based on a person’s training, study or experience and its application to the facts of this particular case, or as to the facts posed by either of the parties as applicable to this particular case, and that absent an application of that training, study or experience to those matters the evidence is unlikely to have cogency, it is appropriate to apply the opinion rule in this case to determining what arrangements would promote the safety, including safety from being subjected to or exposed to family violence, abuse, neglect or other harm, of the child and each person who has the care of the child, whether or not a person has parental responsibility for the child.