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.
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