WebMD Health News
Louise Chang, MD
Sept. 24, 2009 -- Parents who spare the rod just might end up with smarter
Two new studies suggest that children who are spanked have lower IQs than
children who aren't, regardless of where they live.
In one study, researchers analyzed the intelligence scores of roughly 1,500
children in the U.S. who took part in the National Longitudinal Survey of
Youth. They found that these scores were slightly lower among children whose
mothers reported using spanking as a form of discipline.
In the other study, national average IQ scores were found to be lower in
countries where spanking is common.
The research was led by University of New Hampshire sociologist Murray A.
Straus, PhD, who has studied the impact of corporal punishment on child
development for decades. He is a vocal opponent of the practice.
Straus was scheduled to present his findings Friday in San Diego at the 14th
International Conference on Violence, Abuse and Trauma.
"The best kept secret of American child psychology is that kids who are not
spanked are the best behaved and do the best in life," he tells WebMD. "You
won't find that in a single child development textbook, but it is true."
In the U.S. investigation, Straus and colleague Mallie J. Paschall, PhD, of
the Pacific Institute for Research and Evaluation analyzed data from 806
children who were 2 to 4 years old at enrollment and 704 children between the
ages of 5 and 9.
The children were tested for intelligence when they entered the trials and
again four years later.
Even after accounting for factors that could influence IQ scores, such as
parental education and socioeconomic status, spanking appeared to have a
negative impact on intelligence.
The IQs of the younger children who were spanked were 5 points lower on
average four years later than those of children of the same age who were not
spanked. Scores among the older children were an average of 2.8 points lower
among spanked children than children who were not spanked.
Straus characterized the impact of spanking on intelligence in the study as
small but significant.
"Many things influence a child's IQ," he says. "This is just one of them,
but it is one that parents can do something about."
In the second study, Straus analyzed data from more than 17,000 university
students in 32 countries who were polled about their parents' use of corporal
punishment. The answers were then compared to national average IQ scores.
Straus says IQ scores were lower in countries in which spanking was more
prevalent, with the strongest association seen when children were spanked from
childhood through their teens.
While numerous studies have linked corporal punishment to aggressive
behavior, far fewer have examined the impact of spanking on intelligence.
But earlier this month, Duke University research scientist Lisa J. Berlin,
PhD, and colleagues also linked early spanking to reduced intelligence in one
of the most rigorously designed studies to ever address the issue.
The researchers questioned 2,500 racially diverse, low-income moms about
their use of spanking as a discipline tool for their toddlers.
They found that children who were spanked at age 1 were more aggressive than
those who weren't by age 2 and they scored lower on tests to assess mental
development at age 3.
"The research as a whole really paints a picture of the detrimental
long-term effects of physical punishment," Berlin tells WebMD. "The message to
parents is find other ways to discipline your children."
A 2002 analysis of 88 spanking studies spanning six decades linked spanking
to 10 negative behaviors including aggression, anti-social behavior, and mental
More than 90% of the studies found spanking to be detrimental, says
developmental psychologist Elizabeth Gershoff, PhD, who conducted the
"Parents spank to decrease bad behavior in the short and long term and to
promote positive behavior," she tells WebMD. "What the research tells us is
that spanking doesn't seem to be doing either of these things."
But critics say that research is highly suspect because it has largely been
conducted by investigators like Straus, Berlin, and Gershoff who strongly
oppose the practice.
In addition, the studies are often criticized for lacking scientific rigor
-- a charge Gershoff acknowledges is hard to counter.
"We can't very well do experiments in which we tell some parents to spank
their children and others not too," she says.
Straus likens the criticism to that leveled at the early studies linking
smoking to lung cancer.
"For years the tobacco industry was able to destroy the studies one by one
because they all had problems," he says. "No single study was truly definitive.
But in the end the Surgeon General concluded that the evidence as a whole just
couldn't be denied."
SOURCES:14th International Conference on Violence, Abuse and Trauma, San Diego,
Sept. 25, 2009.Murray A. Straus, PhD, professor of sociology and co-director, Family
Research Laboratory, University of New Hampshire, Durham.Lisa J. Berlin, PhD, research scientist, Center for Child and Family Policy,
Duke University, Durham, N.C.Elizabeth Thompson Gershoff, PhD, associate professor, human development and
family sciences, University of Texas at Austin.Straus, M. Journal of Aggression, Maltreatment & Trauma, 2009;
vol 18: pp 459-483.Berlin, L.J. Child Development, Sept-Oct, 2009; vol 80: pp
1403-1420.Gershoff, E.T. Psychological Bulletin, July 2002.
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