Forget fast food – air pollution could be causing childhood obesity (?)

Groan!  These stupid studies of roadside pollution never stop coming out.  This latest one ("Longitudinal associations of in utero and early life near-roadway air pollution with trajectories of childhood body mass index") is a wonderful example of sophisticated statistics being wasted on crap data.

The authors went to great trouble to get defensible data but ignored the elephant in the room:  income.  The people who live by busy roads are generally those who can afford no better:  The poor.  So this is a study of poverty.  And that poor people have worse health in all sorts of ways  is probably the most frequent finding in health research.  So their findings are most parsimoniously explained as yet another demonstration that poor people have worse health.  There is no need to invoke nitrogen oxide exposure as an explanation of anything.  Their findings prove NOTHING about NOx exposure. They are just an example of the hoary statistical fallacy that correlation is causation.

Note this recent study: "It’s poverty, not individual choice, that is driving extraordinary obesity levels"

Had they gathered a measure of income for each family they would have been able to use various statistical techniques (I personally like partial correlation) to remove the effect of income and see if there was anything else left to explain.  But they had no measure of income so could not do that.  If they had such data my guess would be that their quite weak effects would have vanished entirely once the effect of poverty was removed.

They did have a measure of education but some well educated people are poor and some poorly educated people are rich.  Bill Gates was a dropout and there are plenty of Ph.D. burger flippers around these days.  So education is not a reliable proxy for income.

The intellectual level of pollution researchers seems to be permanently stuck in the basement.  If a student had handed this in to me for an assignment, I would have failed it

Exposing children to nitrogen dioxide air pollution from vehicles in the early stages of their life could increase the risk of them becoming obese.

The new research, lead by a team from the University of Southern California and published in the Environmental Health journal, studied 2,318 children the region to see whether there was a link.

It found children living on or near busy main roads in the first year of their life were almost a kilogramme heavier by the age of 10 than those with low exposure.

The scientists were not able to examine how the harmful chemicals increased weight gain in the children but said inflammation of the brain could have caused anxiety-induced overeating and changes in fat metabolism..

They said other factors such as gender, ethnicity and parental education are unlikely that variations in diet could explain the strong link found.

A recent report suggested spending a long weekend in some of Europe’s famous cities could have the same health impacts as smoking up to four cigarettes.


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