New Research on Spanking Might Need a Time Out

Carl Bialik, Wall Street Journal, October 14, 2009

Three recent, widely reported studies on spanking children claimed to show that the disciplinary practice impairs cognitive development in children. {snip}

Yet the three aren’t likely to resolve anything. Many statisticians say they find in them less a firm conclusion than further proof of the difficulty of measuring spanking’s impact.

{snip}

But researchers noted that the study didn’t remove all possible explanations for why some children develop faster than others, such as their parents’ intelligence. Dr. Berlin used maternal educational levels as an imperfect proxy for parents’ intelligence.

Daniel Mundfrom, a statistician at New Mexico State University in Las Cruces, says that even without accounting for other factors, spanking at age 1 explained less than 1% of the variation in cognitive ability at age 3. In other words, maybe spanking does lower intelligence, but not by much.

{snip}

In one peer-reviewed study, published in the Journal of Aggression, Maltreatment, and Trauma, Prof. Straus [Murray Straus, a sociologist at the University of New Hampshire] and Prevention Research Center senior research scientist Mallie J. Paschall examined how 1,510 children were disciplined and how they scored on standardized cognition tests.

The researchers found that children aged 2 to 4 who weren’t spanked gained an average of five points, equivalent to points on an IQ test, four years later compared with those who had been spanked three times or more per week.

{snip}

A second study of his [Straus’s], which was widely reported in the press and presented at a conference about violence, shows that people in countries where spanking is most prevalent have lower average IQs.

Prof. Straus concedes that the methodology was flawed and that spanking may not account for the differences in average national IQs. He says he presented the data on national IQ in part because it corroborated his other study. “The questionable statistics are so consistent with the statistics in the other paper,” he says, adding that his second study can provide “a field day writing about questionable statistics.”

Some statisticians agree. For one thing, the results are skewed by a relatively small number of countries with high rates of spanking and especially low average IQs, particularly Tanzania and South Africa–where about a third of university students reported being spanked a lot before age 12, and where average IQ rates stood at 72. Excluding these countries, “the line would be much closer to flat, indicating little or no relationship,” says Dr. Mundfrom.

Attributing cognitive problems in children to spanking is hard enough. But then saying it is a major reason behind the lower IQ of a nation’s entire population is even trickier because there could be a new raft of potential causes.

Martin Wells, a statistician at Cornell University, re-ran the statistical test to check whether regional variations in IQ–which is lower in Latin America and Africa–could account for the IQ differences Prof. Straus found. After accounting for regional variations, Dr. Wells found the effect of spanking vanished. Dr. Wells plans to use the Prof. Straus’s research in the classroom to demonstrate why it is important to consider alternative explanations.

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