CRD Guidance for Undertaking Systematic Reviews in Health Care
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CRD’s original guidance for undertaking systematic reviews was first published in 1996 and revised in 2001. The guidance is widely used, both nationally and internationally. The purpose of this third updated and expanded edition remains to provide practical guidance for undertaking systematic reviews evaluating the effects of health interventions. It presents the different stages of the process and incorporates issues specific to reviews of diagnostic and prognostic tests, public health interventions, adverse effects and economic evaluations. Recognising that health care decision-making often involves complex questions that go beyond ‘does it work’, the guidance also includes information relating to how and why an intervention works. CRD is part of the National Institute for Health Research (NIHR) and is a department of the University of York, UK. CRD was established in 1994 and undertakes systematic reviews evaluating the effects of interventions used in health and social care. ISBN 978-1-900991-19-3 Centre for Reviews and Dissemination University of York Heslington SAMPLE York YO10 5DD United Kingdom 9 781900 991193 www.york.ac.uk/inst/crd Systematic Reviews CRD’s guidance for undertaking reviews in health care CCRDRD SSystematicystematic RReviews.inddeviews.indd 228383 88/1/09/1/09 009:29:569:29:56 © Centre for Reviews and Dissemination, University of York, 2008 Published by CRD, University of York January 2009 ISBN 978-1-900640-47-3 This publication presents independent guidance produced by the Centre for Reviews and Dissemination (CRD). The views expressed in this publication are those of CRD and not necessarily those of the NHS, the NIHR or the Department of Health. All rights reserved. Reproduction of this book by photocopying or electronic means for non-commercial purposes is permitted. Otherwise, no part of this book may be reproduced, adapted, stored in a retrieval system or transmitted by any means, electronic, mechanical, photocopying, or otherwise without the prior written permission of CRD. Cover design by yo-yo.uk.com Prepared and printed by: York Publishing Services Ltd 64 Hallfi eld Road Layerthorpe York YO31 7ZQ Tel: 01904 431213 Website: www.yps-publishing.co.uk CCRDRD SSystematicystematic RReviews.inddeviews.indd 228484 88/1/09/1/09 009:29:569:29:56 Contents Preface v Acknowledgements ix Chapter 1 Core principles and methods for conducting a systematic review of health interventions 1 Chapter 2 Systematic reviews of clinical tests 109 Chapter 3 Systematic reviews of public health interventions 157 Chapter 4 Systematic reviews of adverse effects 177 Chapter 5 Systematic reviews of economic evaluations 199 Chapter 6 Incorporating qualitative evidence in or alongside effectiveness reviews 219 APPENDICES: Appendix 1 Other review approaches 239 Appendix 2 Example search strategy to identify studies from electronic databases 243 Appendix 3 Documenting the search process 249 Appendix 4 Searching for adverse effects 253 Abbreviations 255 Glossary 261 Index 277 CCRDRD SSystematicystematic RReviews.inddeviews.indd 228585 88/1/09/1/09 009:29:569:29:56 CCRDRD SSystematicystematic RReviews.inddeviews.indd 228686 88/1/09/1/09 009:29:569:29:56 PREFACE This third edition of the Centre for Reviews and Dissemination (CRD) guidance for undertaking systematic reviews builds on previous editions published in 1996 and 2001. Our guidance continues to be recommended as a source of good practice by agencies such as the National Institute for Health Research Health Technology Assessment (NIHR HTA) programme, and the National Institute for Health and Clinical Excellence (NICE), and has been used widely both nationally and internationally. Our aim is to promote high standards in commissioning and conduct, by providing practical guidance for undertaking systematic reviews evaluating the effects of health interventions. WHY SYSTEMATIC REVIEWS ARE NEEDED Health care decisions for individual patients and for public policy should be informed by the best available research evidence. Practitioners and decision-makers are encouraged to make use of the latest research and information about best practice, and to ensure that decisions are demonstrably rooted in this knowledge.1, 2 However, this can be diffi cult given the large amounts of information generated by individual studies which may be biased, methodologically fl awed, time and context dependent, and can be misinterpreted and misrepresented.3 Furthermore, individual studies can reach confl icting conclusions. This disparity may be because of biases or differences in the way the studies were designed or conducted, or simply due to the play of chance. In such situations, it is not always clear which results are the most reliable, or which should be used as the basis for practice and policy decisions.4 Systematic reviews aim to identify, evaluate and summarise the fi ndings of all relevant individual studies, thereby making the available evidence more accessible to decision- makers. When appropriate, combining the results of several studies gives a more reliable and precise estimate of an intervention’s effectiveness than one study alone.5-8 Systematic reviews adhere to a strict scientifi c design based on explicit, pre-specifi ed and reproducible methods. Because of this, when carried out well, they provide reliable estimates about the effects of interventions so that conclusions are defensible. As well as setting out what we know about a particular intervention, systematic reviews can also demonstrate where knowledge is lacking.4, 9 This can then be used to guide future research.10 WHAT IS COVERED IN THE GUIDANCE The methods and steps necessary to conduct a systematic review are presented in a core chapter (Chapter 1). Additional issues specifi c to reviews in more specialised topic areas, such as clinical tests (diagnostic, screening and prognostic), and public health are addressed in separate, complementary chapters (Chapters 2-3). We also consider questions relating to harm (Chapter 4) costs (Chapter 5) and how and why interventions work (Chapter 6). v CCRDRD SSystematicystematic RReviews.inddeviews.indd 228787 88/1/09/1/09 009:29:579:29:57 Systematic Reviews This guide focuses on the methods relating to use of aggregate study level data. Although discussed briefl y in relevant sections, individual patient data (IPD) meta- analysis, which is a specifi c method of systematic review, is not described in detail. The basic principles are outlined in Appendix 1 and more detailed guidance can be found in the Cochrane Handbook11 and specialist texts.12, 13 Similarly, other forms of evidence synthesis including prospective meta-analysis, reviews of reviews, and scoping reviews are beyond the scope of this guidance but are described briefl y in Appendix 1. WHO SHOULD USE THIS GUIDE The guidance has been written for those with an understanding of health research but who are new to systematic reviews; those with some experience but who want to learn more; and for commissioners. We hope that experienced systematic reviewers will also fi nd this guidance of value; for example when planning a review in an area that is unfamiliar or with an expanded scope. This guidance might also be useful to those who need to evaluate the quality of systematic reviews, including, for example, anyone with responsibility for implementing systematic review fi ndings. Given the purpose of the guidance, the audience it is designed for, and the aim to remain concise, it has been necessary to strike a balance between the wide scope covered and the level of detail and discussion included. In addition to providing references to support statements and discussions, recommended reading of more specialist works such as the Cochrane Handbook,14 Systematic Reviews in the Social Sciences,4 and Systematic Reviews in Health Care15 have been given throughout the text. HOW TO USE THIS GUIDE The core methods for carrying out any systematic review are given in Chapter 1 which can be read from start to fi nish as an introduction to the review process, followed step by step while undertaking a review, or specifi c sections can be referred to individually. In view of this, and the sometimes iterative nature of the review process, occasional repetition and cross referencing between sections has been necessary. Chapters 2-5 provide supplementary information relevant to conducting reviews in more specialised topic areas. To minimize repetition, they simply highlight the differences or additional considerations pertinent to their speciality and should be used in conjunction with the core principles set out in Chapter 1. Chapter 6 provides guidance on the identifi cation, assessment and synthesis of qualitative studies to help explain, interpret and implement the fi ndings from effectiveness reviews. This refl ects the growing recognition of the contribution that qualitative research can make to reviews of effectiveness. vi CCRDRD SSystematicystematic RReviews.inddeviews.indd 228888 88/1/09/1/09 009:29:579:29:57 Preface For the purposes of space and readability: The term ‘review’ is used throughout this guidance and should be taken as a short form for ‘systematic review’, except where it is explicitly stated that non-systematic reviews are being discussed. ‘Review question’ is used in the singular even though frequently there may be more than one question or objective set. The same process applies to each and every question. A glossary of terms has been provided to ensure a clear understanding of the use of those terms in the context of this guidance and to facilitate ease of reference for the reader. REFERENCES 1. Bullock H, Mountford J, Stanley R. Better policy-making. London: Centre for Management and Policy Studies; 2001. 2. Strategic Policy Making Team. Professional policy making for the twenty fi rst century. London: Cabinet Offi ce; 1999. 3. Wilson P, Petticrew M, and on behalf of the Medical Research Council’s Population Health Sciences Research Network knowledge transfer project team. Why promote the fi ndings of single research studies? BMJ 2008;336:722. 4. Petticrew M, Roberts H.