I compared my dataset and their data, and it turns out that even in Brazil there is significant correlation between mother education and breastfeeding, barely less so than on the dataset I have. So you should probably disregard my edit in the above post: accounting for confounders could be important in both cases.
I came to comment on the headline, basically to say that "Breastfeeding 'linked to higher IQ'" sounds awfully backwards -- surely this isn't really a result "in favour of" breastfeeding, but rather pretty damning evidence against formulas/substitutes ?
I like your formulation much better:
> children who were not breastfed have an IQ impairment
I could control for demographic factors, but not for other major important factors in a child's development -- parental IQ or views regarding parenting are huge factors in a child's IQ, and they may also influence the decision of whether or not to breastfeed. If parenting books unanimously decided that formula was bad, then parents who cared enough about their children to read them and follow their advice would be more likely to breastfeed and you would see a positive correlation with IQ, even if formula was completely equivalent to breastfeeding.
So while there is a clear correlation after controlling for demographic, there is not necessarily a causation. My formulation really wasn't meant to imply causation, but rather the handling of unknown data (I grouped unknown-status children together with breastfed children). When talking about correlation, it's not meaningful to make a distinction between IQ impairment and IQ gain.
Who organized that contest ?
http://community.topcoder.com/longcontest/?module=ViewProble...
I ended up 5th, and yeah - the demographic variables are by far the most importants.
As Buffett used to say - it's an 'ovarian lottery' and you better have luck at it.
But 1-3 IQ points doesn't seem much, right? I mean, what difference would it make in real life activities?
Also it's just one relatively simple thing. Imagine we find several things that can all increase IQ by a couple points...
I can imagine that merely the act of measuring IQ has significant effect on the population. I can not imagine a population that exists without it, but I imagine it would also have a huge effect on society, as you similarly hypothesize about the 1-3 point increase across the population globally.
Not only that, but are people even still using IQ as a metric of intelligence? As I understand it IQ is only a measure of one type of intelligence. I mean I'm all for giving a child every advantage you can fathom as a parent, so I think this is still kind of cool research, but I don't see how it equates to anything truly meaningful.
It kind of just adds one more point in the "breastfeeding is good" column.
I'm kidding, btw.
If they accept I'll have an opportunity to look deeper -- it's one thing to develop an efficient model, but fully exploiting it in order to gain a better understanding of the data takes some work. A limitation of these contests is that you're rewarded for producing a very efficient model, but there is very little emphasis on analysis of your model once you built it. I think it's a shame, because the person who built the model is often in the best position to have a good intuition of both the dataset and why the model had to be built that way.
I've been considering opening a blog, but I haven't found time to do so yet.
Briefly, the purpose of the contest wasn't to understand the effect of breastfeeding, but to understand how important normal child growth is to mental development. They included several scenarios: with all data available, with demographic data removed, and with demographic data and growth curves removed. Unfortunately, IQ is so overwhemingly affected by demographic that the scenarios without demographic data devolved into a game of extracting all the demographic data that was leaked by non-demographic variables. And when demographic data is available, more than 90% of the variance extracted by the model comes from demographic data rather than biological measurements!
It's really disheartening to think that depending on the social setting you come from, you start with an IQ of 85 or 115 -- at age 7...
After reading the article I did some very quick computations and my finding based on the model I developed is that children who were not breastfed have an IQ impairment in the 1-3 IQ points range, after accounting for confounding factors.
This is very consistent with the results published here.
Compared to this study, I believe the methodology I'm using is more powerful for three reasons:
- much larger sample size: the dataset I have access to comprises 12015 children, compared to 3493 for the study
- a larger set of confounding factors is accounted for: notably, the data includes height and weight measurements at up to five points in time
- confounding factors are fully accounted for, rather than hand-waved away. This is a complex model based on random forests and linear model, and the results are entirely cross-validated.
Stay tuned for more detailed computations. I will also ask the organizers for the exact definition of breastfeeding used.
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Edit:
On the other hand, the study is still very appealing because according to the authors, there is little correlation between demographics and breastfeeding in Brazil, whereas the validity of the effect I'm reporting is dependent on whether the demographic model is powerful enough to remove the correlation. Still, I believe most of the correlation is easy to remove, and it isn't clear that there aren't subtle demographic effects even in Brazil. In particular, the proportion of participants with missing IQ data seems to decrease with duration of breastfeeding, and I don't know if they have an explanation for that.