But is it causal? Defining causality

As I alluded to in my last post, defining what it means for $X$ to cause $Y$ is no simple task.  It is not an idea that can be defined in purely probabilistic terms, because it says something about the mechanisms underlying the system we are studying, and what will happen if we interfere with that system in some way.

Consider the example given at the end of the last post.  The headline was:

How a short nap can raise the risk of diabetes

The implication of this is that the risk of diabetes increases because of the nap.  But what does this mean?

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.

National Traits and the Ecological Fallacy

This article caught my eye, headlined "Why criminals believe in heaven." [The Daily Mail's 'Science' and 'Health' pages are an unlimited resource for writing blog posts about bad statistics, but I promise to try not to only pick on them in future.]

The original paper is here (predictably the DM don't bother to link to it), and here is the university's press release which has been pretty slavishly copied to create the article.   The summary is, the researchers combined crime data from one source (the United Nations Office on Drugs and Crime), with survey data on people's attitudes to religion and other things (from World Values Surveys and European Value Surveys).  They found that the belief in heaven and hell is a strong predictor of crime rates at a country-wide level, whilst rates of particular religious beliefs were not.

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.

Fast food, dodgy infographics, implausible claims

The Daily Mail reported on Wednesday that US restaurant portion sizes had quadrupled(!) since the 1950s, a claim faithfully reproduced from the Center for Disease Control's (CDC) website.  The article comes complete with this infographic.

Now, it should be immediately obvious (if you remember your GCSE maths) that something is not quite right with this picture: the fountain soda looks truly enormous.  Taking the numbers in the diagram on faith for the moment (but see below), the volume of a cup has increased from 7 oz (200 ml) to 42 oz (1.25 l), a worrying factor of six increase.  In accordance with this, the 'NOW' cup on the diagram is 6 times taller than the 1950s cup.