From Medscape Medical News (Presentated in San Diego)

Spanking Linked to Lower IQ in Children
Janis C. Kelly

September 24, 2009 — Groundbreaking research suggests children who are spanked have lower IQs than those who are not, and that the difference is large enough to lower national IQ scores in countries where corporal punishment of children is routine.

Murray Straus, PhD, head of the Family Research Laboratory at the University of New Hampshire, Durham, told Medscape Psychiatry that his landmark 32-nation study of corporal punishment by parents and IQ also suggests that recent increases in IQ in many nations may have been partly a result of the worldwide decrease in the use of corporal punishment by parents.

"The longitudinal part of our study showed that children who were spanked the most fell behind the average IQ development curve, and those who were never spanked advanced ahead of the average," Dr. Straus said. He presented his results at the 14th International Conference on Violence, Abuse and Trauma in San Diego, California.

"That suggested to us that nations that use more corporal punishment of children would have more kids falling behind what they could have achieved, which might result in lower average national IQ, and that is what we found when we looked at data from 32 countries," he added.

To determine the longitudinal effects of spanking, Dr. Straus and colleague Mallie Paschall, PhD, senior research scientist at the Pacific Institute for Research and Evaluation, studied nationally representative US samples of 806 children aged 2 to 4 years and 704 children aged 5 to 9 years. Both groups were retested 4 years later. The IQs of children aged 2 to 4 years who were not spanked were 5 points higher 4 years later than the IQs of those who were spanked.

The IQs of children aged 5 to 9 years who were not spanked were 2.8 points higher 4 years later than the IQs of children the same age who were spanked.

Slows Mental Development

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

Next the researchers examined data from the 32-nation International Dating Violence Study, which included 17,404 students at 68 universities in 32 nations. This study included 2 questions asked to assess experiences of corporal punishment:

* "I was spanked or hit a lot by my parents before age 12."

* "When I was a teenager, I was hit a lot by my mother or father."

Possible responses were strongly disagree, disagree, agree, and strongly agree.

The researchers used the percentage of students who agreed or strongly agreed to estimate the corporal punishment rate in each nation. They then correlated those rates with data on national average IQ. The analysis controlled for 10 variables including mother's education level and socioeconomic status.

The analysis showed a lower national average IQ in nations where spanking was more prevalent. Dr. Straus said that the strongest link between corporal punishment and IQ was for those whose parents continued to use corporal punishment even when subjects were teenagers.

"I was surprised that this link was so strong," Dr. Straus said. "It was logical, but lots of logical things don't work out."

Economic Implications

The correlation between corporal punishment and IQ has major economic implications, as several studies have shown that gross domestic product is closely related to national average IQ, Dr. Straus said.

The researchers suggest 2 possible explanations for the association between corporal punishment and lower IQ. First, corporal punishment is extremely stressful and can become a chronic stressor for young children, who typically experience corporal punishment 3 or more times a week. For many, it continues for years. Research shows that the stress of corporal punishment shows up as an increase in posttraumatic 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," Dr. Straus said.

"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 added.

Problem Child? Ask Whether Parents Are Spanking

Dr. Straus says the findings have immediate clinical implications. One of the first things physicians should do when working with a child who has behavioral problems is to ask the parents about spanking.

If parents are spanking in an attempt to control behavior, they need to be told this is not effective and only serves to model an aversive style of interaction, said Dr. Straus. Instead, clinicians should ask how much punitive vs positive discipline is applied.

"You want to shift the balance away from punitive discipline, such as corporal punishment or verbal violence...toward positive discipline, such as explaining, praising, and rewarding the kid, and not just paying attention when the child is doing something wrong," said Dr. Straus. Dr. Straus strongly emphasized that foregoing punitive discipline does not mean halting other forms of discipline. He also noted that "one of the most closely held secrets in child psychology" is that with children age 2 years or under, no form of discipline really works.

"The recidivism rate for bad behavior is about 50% within 2 hours and 100% within 24 hours in 2-year-olds," Dr. Straus said. "This is true no matter what you do, because those children might understand that what they have done is wrong, but they do not have the developmental control of their behavior that enables them not to repeat it. With 2-year-olds, you just have to be consistent and keep using positive discipline over and over."

Correlation Clear, Cause Uncertain

Elizabeth Gershoff, PhD, associate professor in the Department of Human Development and Family Sciences, University of Texas at Austin, who herself conducted research into the effects of corporal punishment by parents on children, told Medscape Psychiatry that Dr. Straus has observed "an interesting association between national levels of corporal punishment of children, experiences of stress, and IQ," but that it is premature to suggest a causal connection.

She noted that other phenomena that might explain why corporal punishment has gone down and IQ has gone up include increasing levels of education. Better-educated parents use less corporal punishment and are more likely to engage in activities that support children's IQ such as reading to them or helping them with homework, she noted.

Dr. Gershoff added that the model Dr. Straus has suggested is in line with previous research, but that the mechanism by which spanking may lead to lower cognitive abilities remains unclear.

"I am cautious about making causal conclusions about what reducing corporal punishment would do at a country level," Dr. Gershoff said. "It is possible that reducing parents' reliance on corporal punishment may improve children's IQ scores, but I would suggest that would only be the case if parents are able to substitute positive and nonpunitive discipline in the place of corporal punishment."

The study was supported by the National Institute of Mental Health and the University of New Hampshire. The authors have disclosed no relevant financial relationships.

14th International Conference on Violence, Abuse and Trauma: Presentation KF3. Presented September 25, 2009.