MONTREAL - Spanking, yelling at, or shaking children could tend to make them more aggressive toward others, a review of 20 years of studies into physical punishment says.

Researchers say in an article published Monday that children who are physically punished tend to be more aggressive toward their parents, siblings, friends and, later, their spouse.

The analysis was conducted by Dr. Joan Durrant of the family medicine and social sciences department at the University of Manitoba and Ron Ensom, of the Children's Hospital of Eastern Ontario.

It was published in the Canadian Medical Association Journal.

"Research showing the risks associated with physical punishment is robust," the researchers wrote.

No study found that physical punishment helped a child develop positively, and a consensus emerged that parents should be helped to learn non-violent and effective methods of discipline. Among those methods are clear communication with the child and applying consequences for misbehaviour.

The authors noted that key measures have helped ease the problem over the years.

They include the banning of physical punishment by 11 countries, following the adoption of the Convention on the Rights of the Child by the United Nations in the 1990s. Those countries were among the 191 of the world's 196 countries who ratified the convention.

"Three forces — research, the convention and law reform — have altered the landscape of physical punishment," the researchers said.

Examples of physical punishment cited were spanking, yelling, slapping or shaking.

The researchers noted that as recently as 20 years ago, physical punishment was generally considered an efficient way to control an unruly child.

"However, this perspective began to change as studies found links between 'normative' physical punishment and child aggression, delinquency and spousal assault," the report says.

"Virtually without exception, these studies found that physical punishment was associated with higher levels of agression against parents, siblings, peers and spouses."

The researchers note that one study of 500 families indicated that children were less likely to challenge adults when parents were trained to stop punishing them physically. Other studies suggested physical punishment was not more effective than positive discipline measures to improve behaviour.

Many of the studies linked physical punishment with mental health problems including depression, anxiety, and drug and alcohol abuse.

Others also tied it to lower academic performance and slower cognitive development.