Young children who spend most of their time being cared for by someone other than their mother are more likely to show behavioural problems, an apparently startling, though reputably based, new US survey has found.

The study suggests that small children who spend more than 30 hours a week in daycare or in the care of a nanny or family relation - anyone other than the mother - were three times more likely to be aggressive, defiant, demanding and disobedient when they went to nursery school or kindergarten.

The study was conducted over 10 years following more than 1,100 children in 10 US cities in a wide range of care settings - including play centres, daycare groups, Kidergarten, with nannies and children cared for by relatives. The researchers claim that the findings were not related to the type or quality of the childcare given or the gender of the child. They also say that the results hold true regardless of the family's socio-economic status.

These conclusions were based on interviews and observational ratings by the children's mothers as well as by those caring for them and nursery school teachers. There is no doubt that the study has unearthed an issue that demands attention, but whether or not it is related to children being cared for by someone other than their mothers within three to four months of birth is questionable.

Univariable research is fraught with all sorts of problems, the most significant being the part played by factors not measured by the study. What is noticeably lacking in the study is any reference to the father. How long is the prejudice going to remain that fathers cannot be the primary carers of children? I would be curious to know if the father was the stay-at-home parent would the children become three times more aggressive?

Nor did the study indicate how many of the children were members of a two-parent, lone parent or reconstituted family. I expect the study to trigger a strong defensive reaction from working mothers, and rightly so.

Though the study claims that the results were not related to the type or quality of childcare received, I doubt that any effort was made to observe the emotional quality of the care children received.

After all, parenting is the most difficult profession of all, requiring commitment, unparalleled self-sacrifice and the skills to cope with the physical, emotional, social, behavioural, intellectual, educational, creative, sexual, recreational and spiritual development of children.

Quite a tall order for any parent, particularly when they also need to keep their own personal development on par with what they would like for their children.

The reality is that parents (and, indeed, childminders and care agencies) can only bring children to the same level of development they have reached themselves. How many parents and others who care for children possess those kinds of resources?

Other factors that the study may have missed are: employed parents who are tired and stressed, marital conflict, the self-esteem level of parents, the self-esteem level of the children studied, the modelling of aggressive behaviours by adults with whom the children interacted, the level of stimulation within the home, and the children's exposure to video, television and Internet violence.

As regards the last issue on the list above, we know that children are affected by the violence they see via the TV, VCR or the Internet, but have we taken it as seriously as when children are actually, rather than virtually, exposed to violence, intimidation, and cruelty?

In the last decade particularly, due to the rise in violent incidents amongst children in Middle America, there is a greater commitment to discovering the root causes of these seemingly unattributable outbreaks of child violence.

It is good and necessary that researchers continue to investigate the causes of violent and aggressive behaviour in children and adults. However, human behaviour is individual, social, complex and multifaceted and a cautious and holistic approach is needed before causes can be truly inferred.

Dr Tony Humphreys is a consultant clinical psychologist and author of The Family, Love It and Leave It