According to the Guardian (and the Daily Mail, Channel 4 News etc etc) we’ve learned that babies fed on demand ‘do better at school’. This makes me sound smug but I learned this a year ago when the first author, Maria Iacovou, presented her paper at Southampton. The original paper was published in the European Journal of Public Health this month.
As an aside, I believe that Iacovou hoped this paper would be published in the BMJ and that this explains the long gap between the time I heard about the research and the time the world heard about it. The BMJ refuses to print anything which has been printed elsewhere, even in working paper or conference paper form. And that explains why I didn’t blog about it straight after Iacovou’s seminar: I was keen to avoid queering her pitch. (An aside within an aside – is it still OK to say that? It doesn’t feel like a Tory peer in the woodpile thing, but it’s slightly closer to Gove’s reference to “welshing” on a deal.)
It’s another illustration of how journals change the way academics work. In my field (social statistics, or possibly political science, depending on how you look at it) it’s common to publish a little at a time: first an internal working paper, then a conference paper, then finally a paper for peer review. It allows us to bounce our ideas off a wider community and test the strength of our assertions before we submit our work for
shredding peer review.
As a still further aside (would that be as far as Outer Mongolia, I wonder?) I very nearly just blogged without asking – which could have caused trouble. Academics facing these journal policies should take care when they present their results – academic blogging isn’t as rare as it used to be and making a presentation could easily be considered ‘publication’.
Back to the point…
Iacovou and Sevilla used ALSPAC data to look at whether scheduled versus demand feeding of infants had any effect on education outcomes for children or mental health outcomes for mothers. The study involved 14,000 mothers in the Bristol area who signed up in the early nineties during a pregnancy. This paper used a sample of some 10,500 children and looked at whether they were fed on demand or to a schedule when they were four weeks old. The outcomes were SATs scores and the answers to questions on maternal well being which were administered twice: when the children were 8 weeks and 3 years old. Mothers who schedule fed were happier and well rested (but suffered no less clinical depression…) than those who demand fed. Babies who were demand fed did better in school than babies who were schedule fed. You can check out the effect sizes for yourself, but they seemed interesting enough to me: the school results were worth 3 or 4 ranking places in a class of 30. Not huge, but not tiny either.
The interesting thing here is to compare babies who were fed to a schedule, babies who were fed on demand and babies whose mothers wished they could feed to a schedule but failed. The mothers who attempted to feed to a schedule but failed had babies who looked like the demand fed babies. It suggests that some of the unobserved heterogeneity between mothers has been accounted for in the research design.
Let’s unpack that a little… Compared to schedule feeders demand feeders were older, owner-occupiers, breastfeeders, were breastfed themselves and read to their children almost daily. Those who desired to schedule feed but couldn’t make it happen looked like their schedule feeding sisters – not like the demand feecders. And yet, the differences in SATs results and maternal well-being seem to divide along the scheduled vs. demand feeding line, rather than along any of the other, better known fault lines. Wouldn’t we expect the children of demand feeders to do better in school because their mothers are smarter and richer than the schedule feeders, rather than because of the way they were fed as babies? If that were the case, the children of failed schedule feeders would be expected to look like the children of successful schedule feeders. Instead, they look like the children of demand feeders.
The study controlled for sex of baby, age of mother, birth order, gestational age, weight, whether the baby spent time in special care, smoking, mode of delivery, and method of feeding (breast vs bottle) amongst other things and STILL found a (statistically significant) difference. So… Is the study any good? Are its findings a good reflection of the world as it is?
It’s a little hard to say. For starters, this is the first paper to address the question of scheduled vs demand feeding (as opposed to breast vs bottle feeding, which has been addressed left, right and centre). With no corroboration, the authors are rightly cautious about their findings, but the story of the failed schedule feeders does make fascinating reading. Still, it’s worth asking a few questions. Is the ALSPAC data good? Are the measures good? Are we absolutely sure that this rather sweet little natural experiment (in combination with standard statistical controls) has accounted for any confounding? In fact the answer to all those questions is ‘no’.
First question… The ALSPAC data is not representative of the UK and it has large levels of non-random non-response. It’s a longitudinal study – that is, the same people are asked questions at different points in time – so drop-out is a real problem. In this case, it seems likely that demand feeders would be over-represented (since they are the kinds of people who are more likely to answer survey questions) which would alter the effect size (making demand feeding look more important than it really is).
Second question… Asking mothers a question when their babies are four weeks old is unlikely to produce reliable results (I type this as a mother of a six week old – believe me on this one!). Also, what mothers do when their babies are four weeks old and what they do when those babies are six weeks, eight weeks, or twelve weeks 0ld may not be that closely related. The key thing here is that we don’t know whether the babies whose mothers failed to schedule feed at four weeks later (and maybe only days or weeks later) successfully introduced a schedule. If failed schedule feeders go on to be successful schedule feeders, we may be looking at a spurious correlation between demand feeding and academic results. Essentially, we need more than one measure of schedule/demand feeding.
Third question… The authors account for as much of the difference between women as they can by using a long list of controls, and by the cunning use of the category ‘failed schedule feeders’. However, there are still many, many differences between women and most especially between babies which are not accounted for by this study. Some babies are easier to feed or easier to settle than others. These relatively placid babies might be easier to put on a feeding schedule but also more (how shall I put this…?) stupid. The relationship would therefore be between low IQ and ease of scheduling, not between high IQ and demand feeding. OK, so that seems unlikely, but it is the kind of ‘folk wisdom’ unhelpfully put about by women whose babies are a total pain in the arse: “Oh, she must be bright – she’s always so interested in the world” translates roughly as “Oh, please let there be some compensation for my horrific sleep deprivation“.
So where does that leave us? For all the potential pitfalls, I still think this is a rather nice study. Preliminary, but rather nice. But you know what’s really, really annoying? I think the Daily Mail article is a better reflection of the original paper than the Guardian article (primarily because it quotes Iacovou explaining that this is the first study of its kind and the result needs to be corroborated from other data). Dammit.