One of the most used examples for teaching rational thinking is the ‘Mediterranean Diet’ story. Put simply this is the idea that Northern Europeans live longer if they stick to the diet of Southern Europeans i.e. Lots of salad and olive oil. A few moment’s thought demonstrates how silly this idea is i.e. Northern Europeans who consume lots of salad and olive oil tend to come from higher income brackets, and it’s the higher economic status that is the predictor of longevity, not the diet itself.
This can to mind when I read a story in the Daily Mail this week:
This story reports a study from the Michigan State University suggesting that students who join an on-campus gym get better grades and stay in university longer. Sadly the original paper is behind a paywall, but the available abstract makes no reference to controlling for the disposable income of the students. (Working in a university I am fortunate that I have access to the full-text of this paper. As I suspected, the study doesn’t control for disposable income, indeed the paper actually acknowledges that Socio-economic status could confound the results) It seems possible that students who can afford to join a gym might have a high disposable income, and indeed that those with a higher disposable income might spend less time in paid employment and thus have more time for sporting activities (and college work !!).
All of this leaves me wondering who is at fault here. It’s interesting that whilst the paper itself acknowledges a potentially dramatic confounding variable it still makes claims about the importance of the relationship found. At times I worry that in a drive to gain publicity for their research scientists may end up actually making matters worse by facilitating a lack of understand that correlation doesn’t necessarily equal causation.
Teaching Rational Thinking 
One Response to “Being a member of a gym makes you do better at University…. The return of the Mediteranean Diet Effect”