If correlation isn't causation, then what is?

I've started to get a little tired of writing entirely about media shenanigans, and in all likelihood so, dear readers, have you tired of reading about them.  So today I'm going to provide one of the 'educational pieces' alluded to in this blog's description; specifically I'm going to start talking about causal inference, which is the driving force behind the research I'm lucky enough to be paid to do.

We hear a lot in statistics classes (if you're inclined to go to them) and places like this blog, that "correlation is not causation."  Packaged within this pithy but stern warning is some very sound advice: just because you observe a relationship between two things doesn't tell you anything about the mechanism (if any) which creates that relationship.

Twins, or In which newspapers mess up odds calculations (again)

This BBC piece interviews a couple who've been 'blessed' with three sets of twins (rather you than me).   The caption states that

Doctors told them the chances of having three sets of twins was 500,000-1.

Doctors that don't know much about genetics, perhaps.

Extreme Comparisons

This is just a fairly short note on what has been covered in other cases elsewhere.  The BBC reported today that Tameside in Greater Manchester is the "UK's heart disease capital".  This is on the basis that the rate of deaths from heart disease between 2009 and 2011 was higher than anywhere else, at 132 per 100,000 people.  The data come from the British Heart Foundation, and I couldn't immediately see how to get at it.

The article mades a particular point of noting that this rate is three times higher than that of Kensington and Chelsea.  This sounds very dramatic, but it really isn't, so don't go moving just yet (even if you can afford a house in Kensington).

Smoking rates: even the 'good guys' shouldn't be trusted

The Guardian reports today that the number of children under 16 (more precisely aged 11-15) taking up smoking has has risen by 50,000 in a single year.  This is a slightly irritating headline simply because the number is without context, but the sub-headline is more helpful: from 157,000 to 207,000, which is quite dramatic: a 32% increase.

First obvious question - is this statistically significant? Well, let's have a look at the research quoted by the Guardian, which comes from Cancer Research UK.  Their Figure 6.10 immediately arouses suspicion.  There does appear to be an uptick in the figures from 2010 to 2011, but they remain below the 2009 figure!  The overall trend in the numbers over the past 10 years is clearly downwards.  So either we believe that the number of children taking up smoking fell and then rose dramatically in consecutive years, or else we might just be witnessing a bit of noise in our data.

Newsflash: everyone being healthier reduces deaths

People like me often complain about the accuracy of scientific journalism, and the selective nature of the reports we see in the media; indeed, there's plenty to complain about.  However it's perfectly possible to misrepresent a story simply by choosing to place a particular spin upon it, usually one which makes the story seem more political than the original research.  It's easy to blame the newspapers for this, but often the problem is compounded by academic press releases, which are themselves designed to catch the eye of media outlets.