Users' Guides to the Medical Literature: A Manual for Evidence-Based Clinical Practice, Second Edition (Jama & Archives Journals)

870 Pages·2008·9.91 MB·English

by  Gordon Guyatt

USERS’ GUIDES
TO THE
MEDICAL
LITERATURE
Notice
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USERS’ GUIDES
TO THE
MEDICAL
LITERATURE
A MANUAL FOR
EVIDENCE-BASED CLINICAL PRACTICE
SECOND EDITION
The Evidence-Based Medicine Working Group
Editors
Gordon Guyatt, MD, MSc Drummond Rennie, MD
Departments of Clinical Epidemiology JAMA
and Biostatistics and Medicine Chicago, Illinois
Faculty of Health Sciences Philip R. Lee Institute for Health Policy
McMaster University Studies
Hamilton, Ontario, Canada University of California, San Francisco
San Francisco, California, USA
Maureen O. Meade, MD, FRCPC, MSc Deborah J. Cook, MD, MSc
Departments of Medicine and Clinical Departments of Medicine and Clinical
Epidemiology and Biostatistics Epidemiology and Biostatistics
Faculty of Health Sciences Faculty of Health Sciences
McMaster University McMaster University
Hamilton, Ontario, Canada Hamilton, Ontario, Canada
New York Chicago San Francisco Lisbon
London Madrid Mexico City Milan
New Delhi San Juan Seoul Singapore
Sydney Toronto
JAMAevidence
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DOI: 10.1036/007159034X
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To our students, in many countries, whose interest, passion,
and probing questions made possible the development of the
methods we use to communicate the concepts of evidence-
based medicine.
GG, MOM, and DJC
To Deb, who has watched over and tended me while I have
watched over and tended this wonderful group of authors,
with gratitude for her love and her good humor.
DR
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CONTENTS
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xi
Foreword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xxi
Part A
The Foundations
1 How to Use the Medical Literature—and This Book—
to Improve Your Patient Care. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 The Philosophy of Evidence-Based Medicine . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3 What Is the Question? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4 Finding the Evidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5 Why Study Results Mislead: Bias and Random Error. . . . . . . . . . . . . . . . . . . . 59
Part B
Therapy
6 Therapy (Randomized Trials). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
7 Does Treatment Lower Risk? Understanding the Results. . . . . . . . . . . . . . . . . 87
8 Confidence Intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
9 Advanced Topics in the Validity of Therapy Trials
9.1 An Illustration of Bias and Random Error. . . . . . . . . . . . . . . . . . . . . . . 109
9.2 Surprising Results of Randomized Trials . . . . . . . . . . . . . . . . . . . . . . . 113
9.3 Randomized Trials Stopped Early for Benefit. . . . . . . . . . . . . . . . . . . . 153
9.4 The Principle of Intention to Treat . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
9.5 N-of-1 Randomized Controlled Trials. . . . . . . . . . . . . . . . . . . . . . . . . . 179
9.6 Clinical Decision Support Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
10 Advanced Topics in the Results of Therapy Trials
10.1 Hypothesis Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
10.2 Understanding the Results: More About Odds Ratios . . . . . . . . . . . . . 221
10.3 What Determines the Width of the Confidence Interval? . . . . . . . . . . 231
vii
viii
CONTENTS
10.4 Composite Endpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
10.5 Measuring Patients’ Experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
11 Advanced Topics in Applying the Results of Therapy Trials
11.1 Applying Results to Individual Patients. . . . . . . . . . . . . . . . . . . . . . . . . 273
11.2 Example Numbers Needed to Treat. . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
11.3 Dealing With Misleading Presentations of Clinical
Trial Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
11.4 Surrogate Outcomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
11.5 Qualitative Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
Part C
Harm (Observational Studies)
12 Harm (Observational Studies) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
13 Advanced Topics in Harm: Correlation and Regression . . . . . . . . . . . . . . . . 383
Part D
Diagnosis
14 The Process of Diagnosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399
15 Differential Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407
16 Diagnostic Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419
17 Advanced Topics in Diagnosis
17.1 Spectrum Bias. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439
17.2 Examples of Likelihood Ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
17.3 Measuring Agreement Beyond Chance . . . . . . . . . . . . . . . . . . . . . . . . . 481
17.4 Clinical Prediction Rules. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491
Part E
Prognosis
18 Prognosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509