The higher the percent of parents in a nation who used corporal punishment with teenagers, the lower the national average IQ. Credit: Murray Straus

Children who are spanked have lower IQs worldwide, including in the United States, according to new groundbreaking research by University of New Hampshire professor Murray Straus. The research results will be presented Friday, Sept. 25, 2009, at the 14th International Conference on Violence, Abuse and Trauma, in San Diego, Calif.

The higher the percent of parents in a nation who used corporal punishment with teenagers, the lower the national average IQ. Credit: Murray Straus

"It is time for psychologists to recognize the need to help parents end the use of corporal punishment and incorporate that objective into their teaching and clinical practice. It also is time for the United States to begin making the advantages of not spanking a public health and child welfare focus, and eventually enact federal no-spanking legislation," he says.

IQ and Spanking in America

American children who were spanked had a lower cognitive ability score four years later. Credit: Murray Straus

Straus found that children in the United States who were spanked had lower IQs four years later than those who were not spanked.

American children who were spanked had a lower cognitive ability score four years later. Credit: Murray Straus

Straus and Mallie Paschall, senior research scientist at the Pacific Institute for Research and Evaluation, studied nationally representative samples of 806 children ages 2 to 4, and 704 ages 5 to 9. Both groups were retested four years later.

IQs of children ages 2 to 4 who were not spanked were 5 points higher four years later than the IQs of those who were spanked. The IQs of children ages 5 to 9 years old who were not spanked were 2.8 points higher four years later than the IQs of children the same age who were spanked.

"How often parents spanked made a difference. The more spanking the, the slower the development of the child's mental ability. But even small amounts of spanking made a difference," Straus says.

IQ and Spanking Worldwide

Straus also found a lower national average IQ in nations in which spanking was more prevalent. His analysis indicates the strongest link between corporal punishment and IQ was for those whose parents continued to use corporal punishment even when they were teenagers.

Straus and colleagues in 32 nations used data on corporal punishment experienced by 17,404 university students when they were children.

According to Straus, there are two explanations for the relation of corporal punishment to lower IQ.

The More Spanking, the Greater the Probability of Post-Traumatic Stress Symptoms.

First, corporal punishment is extremely stressful and can become a chronic stressor for young children, who typically experience corporal punishment three or more times a week. For many it continues for years. The research found that the stress of corporal punishment shows up as an increase in post-traumatic stress symptoms such as being fearful that terrible things are about to happen and being easily startled. These symptoms are associated with lower IQ.

Second, a higher national level of economic development underlies both fewer parents using corporal punishment and a higher national IQ.

The good news is that the use of corporal punishment has been decreasing worldwide, which may signal future gains in IQ across the globe.

"The worldwide trend away from corporal punishment is most clearly reflected in the 24 nations that legally banned corporal punishment by 2009. Both the European Union and the United Nations have called on all member nations to prohibit corporal punishment by parents. Some of the 24 nations that prohibit corporal punishment by parents have made vigorous efforts to inform the public and assist parents in managing their children. In others little has been done to implement the prohibition," Straus says.

"Nevertheless, there is evidence that attitudes favoring corporal punishment and actual use of corporal punishment have been declining even in nations that have done little to implement the law and in nations which have not prohibited corporal punishment," he says.