Parental favouritism - showing a preference for one child over another - has an equally negative impact on both favoured and disfavoured children, according to a University of Queensland study.
The study was conducted by Dr Grania Sheehan, now a research fellow with the Australian Institute for Family Studies.
For her PhD with the School of Psychology, Dr Sheehan observed family interaction and conflict resolution in 200 families of adolescent twins aged between 12 and 18.
She found favoured and disfavoured children resolved sibling conflict in destructive ways compared to children in families where there was no favouritism.
For example, favoured and disfavoured children were more aggressive towards their sibling, avoided resolving sibling conflict and engaged in less problem-solving behaviour during sibling conflict than children who reported equal treatment.
"There was also more distress experienced by both children after an argument. Fighting among siblings is commonplace and is an important means of learning conflict resolution," Dr Sheehan said.
"However, parental favouritism causes the experience to be particularly painful and equally negative for both the favoured and disfavoured siblings."
The study, to be presented at the International Conference on Personal Relationships 2000 in Brisbane in late June, is the first in Australia to examine the relationship mechanisms through which parental favouritism shapes children's development.
Dr Sheehan said her study also found that children in families where parental favouritism existed viewed their parents more negatively.
She said while it was generally normal and appropriate that parents used different techniques to raise different children, problems arose when they began exhibiting strong preferences for particular children, or when the child believed he or she had been treated unfairly in comparison with their sibling.
She said favouritism could take many forms including sharing feelings, thoughts and activities with one child more than another, and using control mechanisms such as punishment, behaviour monitoring or criticism more on one child than on another.
"Using twins for the study controlled for other factors that can result in different parenting techniques such as age, birth order and gender," Dr Sheehan said.
Dr Sheehan said extreme cases of parental favouritism were often linked to high levels of family dysfunction and marital dissatisfaction - creating an environment where both siblings suffered not just the child who was disfavoured.
For more information, contact Dr Grania Sheehan (telephone 03 9214 7865 until 5pm Monday, June 26, or 07 3844 8740 after that time), conference organiser Sally Brown (telephone 07 3201 2808) or Shirley Glaister at UQ Communications (telephone 07 3365 2339).