Statistics

Ricardo just sent me a link to the British Heart Foundation statistics website. It's a goldmine. They have data on just about every aspect of health and lifestyle in the U.K. I find it very empowering to have access to this kind of information on the internet.

I've just started sifting through it, but something caught my eye. The U.K. is experiencing an obesity epidemic similar to the U.S.:
Here's where it gets interesting. This should look familiar:

Hmm, those trends look remarkably similar. Just like in the U.S, the British are exercising more and getting fatter with each passing year. In fact, maybe exercise causes obesity. Let's see if there's any correlation between the two. I'm going to plot obesity on the X-axis and exercise on the Y-axis to see if there's a correlation. The data points only overlap on three years: 1998, 2003 and 2006. Let's take a look:
By golly, we've proven that exercise causes obesity! Clearly, the more people exercise, the fatter they get. The R-value is a measure of how closely the points fall on the best-fit line. 0.82 isn't bad for this type of data. If only we could get all British citizens to become couch potatoes, obesity would be a thing of the past! OK, I'm kidding. The obesity is obviously caused by something else. I'm illustrating the point that correlations can sometimes be misleading. Even if an association conforms to our preconceived notions of how the world works, that does not necessarily justify saying one factor causes another.  Controlled experiments can often help us strengthen a claim of causality.