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Towards evidence based medicine for paediatricians
  1. Edited by Bob Phillips

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Archimedes seeks to assist practising clinicians by providing “evidence based” answers to common questions that are not at the forefront of research but are at the core of practice (format adapted from BestBETs published in the Emergency Medicine Journal). A full description of the format is available online at

Readers wishing to submit their own questions—with best evidence answers—are encouraged to review those already proposed at If your question still hasn’t been answered, feel free to submit your summary according to the instructions for authors at

Relative or absolute certainty?

If you were offered a choice of drugs 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 who wouldn’t, and would be happy to just do as they were 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 people 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 above statements all refer to the same underlying difference of treatment success in 20% of patients versus 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 people choose the drug that doubles the success rate. 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.

Bob Phillips; Evidence-based On Call, Centre for Evidence-based Medicine, University Department of Psychiatry, Warneford Hospital, Headington OX3 7JX, UK; bob.phillips{at}

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