Researchers and journalists still challenged by the concept of causation

New analysis of smoking and schizophrenia suggests causal link

Sigh. Sound familiar? This time it’s about tobacco smoke, not marijuana, but the problem is still the same.

In research that turns on its head previous thinking about links between schizophrenia and smoking, scientists say they have found that cigarettes may be a causal factor in the development of psychosis.

After analysing almost 15,000 tobacco users and 273,000 non users and their relative rates of psychosis – where patients can experience delusions, paranoia and hear voices in their heads – the researchers said cigarette smoking appears to increase risk.

It’s the same bad reporting of research that happened with marijuana — and they even mention that they used to use the same argument with marijuana!

Previous studies, some by Murray, have also linked cannabis use to psychosis. But there is much debate about whether this is causal or whether there may be shared genes which predispose people to both cannabis use and schizophrenia.

McCabe said the new results on smoking suggest “it might even be possible that the real villain is tobacco, not cannabis” — since cannabis users often combine the drug with tobacco.

Once again, they’re using a research method that can only show correlation, not causation.

For this study, McCabe’s team analysed rates of smoking in people presenting with their first episode of psychosis and found that 57 per cent of these individuals were smokers.

People with a first episode of psychosis were three times more likely to be smokers than those in the control groups.

The problem is that we don’t know enough about psychosis to know whether there are internal proclivities that exist and can influence behavior before the first “episode” fully manifests.

Here’s how you would determine causation of psychosis:

  • Take a large control group of non-smokers.
  • Make a random half of them start smoking.
  • Follow both groups, and if the smoking group has a significantly higher incidence of psychosis, then you have a fairly good indication of causation.

Of course, such research isn’t possible.

The research that is being done is great, but it doesn’t indicate causality. However, if you want to get published in the press, you need to claim (or at least, imply) causality.

Post to Twitter Post to Facebook Post to Reddit Post to StumbleUpon