A new study out of Flinders University looked at the number of friends that elderly people had in 1992. When they re-contacted the subjects in 2002, they found that those who had more friends were less likely to have died.
So far so good. But the researchers then concluded that having more friends makes you less likely to die. I admit that this might be true. But it might also be the case that healthy people are better able to maintain their friendship networks. As anyone who’s taken a single stats class knows, correlationâ‰ causation. So researchers who only show correlations shouldn’t make unsupportable claims about causation.
This kind of study is a hardy perennial in Australia. The last example I can remember was a Commonwealth Bank Foundation study that found a correlation between financial knowledge and income, and concluded that knowing more about money made you richer (never once stopping to wonder whether rich people might have a bigger incentive to learn more about money management). Again, it might really be the case that knowing more about money makes you richer, but if you don’t have the evidence for it, you should at least acknowledge the possibility of reverse causation.
These aren’t hard issues to comprehend, but it’s amazing that almost no journalists are willing to approach research with a modicum of scepticism, while many researchers are willing to pull the wool over the public’s eyes. As a result, better studies that do try hard to show causation (eg. through randomised trials, natural experiments or instrumental variables) struggle to get airplay.