The Promotion of Breastfeeding Intervention Trial (PROBIT) study of infant feeding and childhood IQ1 is impressive, not least because it brings the benefits of randomization to an area where it was not previously thought feasible or even ethical. However, it may not be the last word on breastfeeding and IQ.
The headline result is a difference in verbal IQ between the experimental and control groups of 7.5 points. This is half a standard deviation and, therefore, a very substantial effect. But is it plausible? We believe it is not.
Der G, Batty GD, Deary IJ. Results From the PROBIT Breastfeeding Trial May Have Been Overinterpreted. Arch Gen Psychiatry. 2008;65(12):1456–1457. doi:10.1001/archpsyc.65.12.1456-b
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