Sometimes, we spot stuff that predicts how things will happen. Well, usually happen. These may be described as ‘risk’ factors – that is, factors which predict something will happen – or ‘prognostic’ factors – thinks that predict the outcome of a condition. There are a range of generalisations that are sometimes made from ‘predictive’ studies, and if you take an extremely non-medical example you may spot some of their weaknesses.

Say someone reports a study that shows a barking dog predicts a herd of small children in the kitchen. The study was done during daytime hours, in a family home on a suburban street. While the barking was a good predictor (85% of the time), it wasn’t perfect, sometimes there was a delivery driver at the door; though preceded by hearing the van drawing up. The authors conclude that those wishing to protect the biscuits in their kitchen should use barking dogs to warn them.
Clearly, this only works in a home that owns a dog, and is unlikely to be applicable if you live in an apartment block, or the barking is well after bedtime. Even if you own a dog, barking while out trekking across fields won’t predict kids in the kitchen (but might well signal another walker). Predictive factors are context specific.

Now if the authors of the dog-child-kitchen study were daft enough to suggest that muzzling the dog would stop little visitors, we’d be laughing at them. Predictive factors are not always causative.

When you’re reading, it’s worth keeping these elements in mind. If you find a predictive factor in one study, be aware that the context may make it unhelpful – or at least, differently indicative – in another. And be very wary of anyone taking a predictive association and using this to makes claims for a treatment.

– Archi