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Towards evidence based medicine for paediatricians
  1. Bob Phillips
  1. Evidence-based On Call, Centre for Evidence-based Medicine, University Dept of Psychiatry, Warneford Hospital, Headington OX3 7JX, UK; bob.phillips{at}doctors.org.uk

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In order to give the best care to patients and families, paediatricians need to integrate the highest quality scientific evidence with clinical expertise and the opinions of the family.1Archimedes seeks to assist practising clinicians by providing “evidence based” answers to common questions which are not at the forefront of research but are at the core of practice. In doing this, we are adapting a format which has been successfully developed by Kevin Macaway-Jones and the group at the Emergency Medicine Journal—“BestBets”.

A word of warning. The topic summaries are not systematic reviews, through they are as exhaustive as a practising clinician can produce. They make no attempt to statistically aggregate the data, nor search the grey, unpublished literature. What Archimedes offers are practical, best evidence based answers to practical, clinical questions.

The format of Archimedes may be familiar. A description of the clinical setting is followed by a structured clinical question. (These aid in focusing the mind, assisting searching,2 and gaining answers.3) A brief report of the search used follows—this has been performed in a hierarchical way, to search for the best quality evidence to answer the question.4 A table provides a summary of the evidence and key points of the critical appraisal. For further information on critical appraisal, and the measures of effect (such as number needed to treat, NNT) books by Sackett5 and Moyer6 may help. To pull the information together, a commentary is provided. But to make it all much more accessible, a box provides the clinical bottom lines.

The electronic edition of this journal contains extra information to each of the published Archimedes topics. The papers summarised in tables are linked, by an interactive table, to more detailed appraisals of the studies. Updates to previously published topics will be available soon from the same site, with links to the original article.

Readers wishing to submit their own questions—with best evidence answers—are encouraged to review those already proposed at www.bestbets.org. If your question still hasn’t been answered, feel free to submit your summary according to the Instructions for Authors at www.archdischild.com. Three topics are covered in this issue of the journal.

  • Are routine chest x ray and ECG examinations helpful in the evaluation of asymptomatic heart murmurs?

  • Does intravenous mannitol improve outcome in cerebral malaria?

  • Do antipyretics prevent febrile convulsions?

The duck-yak problem

It seems to be every other day that a new wonder test arrives. Yesterday it was CRP, tomorrow serum PCT may loom. How do these tests, which in early studies have such astounding sensitivity and specificity, fall by the wayside so quickly? It doesn’t have to be fraud. It may be a reflection of the duck-yak problem.* You see, when tests are first tried out, it’s often in a group of patients with an advanced version of the condition (say, meningococcal septic shock) and compared with levels in a “healthy” population (for example, preoperative blood tests). The test is then very effective at separating those with septic shock (the yaks) from the healthy ones (the ducks). If a test can’t tell the difference between these two groups, it’s truly useless. Clinically though, it’s the next phase study you actually want. These look to see if the new wonder test actually works on the floor of the A&E department. Can it distinguish between children with a few petechiae and a cold, and those who have the early stages of meningococcal septicaemia? Here, the test is asked not to separate the yaks from the ducks but a yak from a moose—and I’m assured by Canadian colleagues this is pretty tough stuff. At this stage, the tests don’t normally perform as well, and another false dawn is over. So the moral of the duck-yak problem is this: don’t ask first about the sensitivity of a new test, ask whether it was tested in an appropriate population.


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The duck-yak problem. Illustration by Jack Maypole, MD

REFERENCES

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Footnotes

  • * Thanks to Killgore Trout

  • Bob Phillips

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