Table 8.1Comparison between reliable and unreliable use of anecdotal evidence

Anecdotal evidence is reliableAnecdotal evidence is unreliable
When the outcomes of the disease or condition are predictable in the absence of treatment (e.g. migraines, chronic arthritic pain, premenstrual tension)When the outcomes of the treatment are uncertain for the individual (e.g. breast cancer, diabetes)
When the effects of the treatment are largeWhen the effects of the treatment are small and subtle
When the effects of the treatment are immediateWhen the effects of the treatment are delayed
When the effects of treatment can be confirmed by repetitionWhen the effects of the treatment cannot be confirmed by repetition
When the effects of treatment can be confirmed by an ‘N of 1’ trialWhen the effects of treatment are disproved by an ‘N of 1’ trial

From: Chapter 8, The weakness of one

Cover of Smart Health Choices
Smart Health Choices: Making Sense of Health Advice.
Irwig L, Irwig J, Trevena L, et al.
London: Hammersmith Press; 2008.
Copyright © 2008, Professor Les Irwig, Judy Irwig, Dr Lyndal Trevena, Melissa Sweet.

All rights reserved. No part of this publication may be reproduced, stored in any retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publishers and copyright holder or in the case of reprographic reproduction in accordance with the terms of licences issued by the appropriate Reprographic Rights Organisation.

PubMed Health. A service of the National Library of Medicine, National Institutes of Health.