Junk food science

One of my favorite ambiguously-hyphenated phrases, but in this example the hyphen definitely goes after the second word.

The Herald tells us (or reprints the Daily Mail telling us):

Children who eat junk food will grow up to have a lower IQ than those who regularly eat fresh, home-cooked cooked meals, a study reveals.

Childhood nutrition has long lasting effects on IQ, even after previous intelligence and wealth and social status are taken into account, according to the paper.

 You’d think from that description that the study looked at children growing up, and that they found effects of meals in the past rather than the present. And that the effects were big.  None of these is the case.

The paper (paywalled) looked at cognitive function tests and meals at ages 3 and 5 for a group of children.  The analysis found that 5-year IQ was related to meals at age 5, but not (or more weakly) to meals at age 3, and, to quote the researchers themselves

 Overall, having more often slow meals accounted for negligible amounts of variance in cognitive change.

where `negligible’ means less than 1%.

You’d also worry about other differences between families that might be associated with IQ-test performance.  The quote tells us that previous intelligence and wealth and social status were taken into account, but the ‘wealth and social status’ in the statistical models was just a single five-point scale, and there’s no way that could reliably account for socio-economic differences.