Does spanking REALLY lower IQ?

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If you're reading this blog, chances are that spanking isn't your first choice when it comes to discipline. Last week, Time magazine ran a report citing Murray Straus' research evidence that kids who are spanked have lower IQs than those who are not. Straus said that, the more kids are spanked, the greater the difference between their IQs and those of their peers - a difference that was found across several countries around the world. The finding is alarming, but the numbers tempered my reaction. Among older kids, the average difference in intelligence was a little under 3 IQ points. As a psychologist who has administered hundreds of IQ tests, I can tell you that this finding is small enough to be considered measurement error. Nonetheless, the U.N. has come out against corporal punishment (or inflicting pain to change behaviour), citing its negative impact on kids. What does the research say? Part of the reason for the recent interest in Straus' results is a study by Straus and Mallie Paschall published in the July 2009 issue of the Journal of Aggression, Maltreatment & Trauma. Over 800 children were assessed at the beginning of the study and again 4 years later, and the researchers controlled for 10 factors that might contribute to differences in the development of cognitive skills. Straus did not measure the children's IQ; in fact, he used three tests (Body Parts Recognition, Memory for Locations, and Motor and Social Development) and combined the results to generate an overall score. Two to four year-olds who were never spanked gained a little over 5 points on the cognitive tests over the 4 years of the study; this increase dropped to zero for those who were punished 3 or more times in a week. Five to nine year-olds who weren't spanked gained 2 points over four years; this dropped to a loss of approximately 1.5 points if they were spanked twice and about 0.9 points if they were spanked more than three times. Straus admitted that the size of the effects were small and that the development of cognitive skills depends on many other factors besides the number of times kids receive corporal punishment. Nonetheless, he indicated that, at the population level, reductions in the use of corporal punishment might account for the rise in IQ scores over the past several decades. No mention was made of improvements in education or nutrition as possible contributors to this effect.

In the May 2004 issue of The Journal of Psychology, researchers from the University of Calgary analyzed data from over 70 studies (including several by Straus) published between 1961 and 2000 on the effects of corporal punishment on kids; together, the research included over 47,000 participants. Their conclusion: corporal punishment has a small, perhaps negligible effect on children's emotional and behavioural functioning, and none at all on their cognitive abilities. Many of the previous studies failed to account for a number of other factors that might affect the relationship between physical punishment and development, including the age when kids were spanked, the frequency, other disciplinary techniques used by the parents, or the quality of the parent-child relationship. Paolucci and Violato, the authors of the meta-analysis, argued that research showing negative effects of corporal punishment should not be ignored, but the findings shouldn't be exaggerated either. They suggested that physical punishment might be one risk factor among many that could, in combination, contribute to negative emotional, behavioural, or cognitive outcomes. Rather than focusing on a single factor, they argued that their results suggest a need to focus on increasing positive parenting behaviours that have been more clearly linked to beneficial outcomes. Note that Straus' study, and those analyzed by Paolucci and Violato, excluded families in which abuse occurred. They worked hard to ensure that their results were not clouded by the impact of child abuse, which has been shown conclusively in research to have myriad negative effects!

Overall, it looks like the impact of corporal punishment at the individual level is small; in fact, it's not even possible to say that spanking causes lower cognitive scores, more behavioural problems, or an increase in emotional concerns, since researchers can't rule out every other possible contributing factor to the picture. As a psychologist who works with families, I was a bit disappointed that the data didn't support the anti-spanking camp more unequivocally. I've always advocated against corporal punishment because it doesn't teach kids the skills they need to behave more appropriately, and it certainly doesn't improve the parent-child relationship. What seems clear is that spanking doesn't contribute to positive outcomes. On the other hand, there are a number of effective parenting strategies to reduce the occurrence of negative behaviour in young kids. 1-2-3 Magic: Effective Discipline for Children 2-12 (123 Magic) is only one of many books with suggestions for parents! 1-2-3 Magic focuses on the effective use of time-out.

You can read Straus' study here.

Paolucci and Violato's study is here.

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