If you were offered a choice of medication to treat an ailment you were suffering from, and you’d asked about how effective they were (and there’s a huge chunk of the population that wouldn’t, and would be happy to just do as they are told), then what information would you like? How much information do you want to know? “It works better than the previous treatments”, or a more mathematical estimate? Would you prefer to be told “For every ten folk I give this drug to, one will benefit?”, or “Taking the drug improves success rates by 10%.” or perhaps “Taking the drug will double your chances of success”?
As you have no doubt figured out, the statements all refer to the same underlying difference of treatment success in 20%, vs 10% in the comparison group. The statements refer to the ‘number needed to treat’, the ‘absolute risk reduction’ and the relative risk. Their ‘truth’ may be actually the same, but the perception of them is strikingly different: the majority of folk choose the drug that doubles the success. Relative risks are almost always chosen over descriptions of absolute improvement, and this is not limited to the ‘general population’ but applies to healthcare professionals too. So how can we use this? We can remember it when we’re being ‘sold at’ by drug reps. We can use it when we’re selling ideas to patients and families (“But the medicine is going to double the chance of success!”) And we can also use it, with care, when we’re discussing issues with managers and budget holders to describe the benefits of interventions we honestly believe will make healthcare better.

Acknowledgement. Photo from cdw9, on flickr