Health & Parenting

Kids Who Get Spanked May Have Lower IQs

Critics Say Evidence Is Weak continued...

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 health issues.

More than 90% of the studies found spanking to be detrimental, says developmental psychologist Elizabeth Gershoff, PhD, who conducted the analysis.

"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."