Iain K. Crombie
University of Dundee Dundee, UK
This second edition first published 2022
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Acknowledgements
I am grateful to the University of Dundee for providing the facilities to research and write the second edition of this book. The success of the first edition was due in no small part to my colleagues for their support and encouragement. As the style and much of the content of this new edition follows the original, I am pleased to be able to thank them again for their help. Special thanks are due to Geraldine Fardon whose constructive comments highlighted imprecise, vague, and confusing text. I take full responsibility for any remaining flaws.
Preface to the First Edition
This book was written to meet the needs of health professionals as medicine moves to be evidence‐based. The initial idea arose during discussion with younger colleagues and students on difficulties of interpreting the medical literature. It quickly became apparent that their needs would be best met by a short book detailing criteria for critical appraisal.
The book is organised in two parts. The first five chapters provide an introduction to critical appraisal of quantitative research, indicating how papers can be read and how the results can be interpreted. Experienced researchers could easily omit these chapters. The final six chapters provide annotated checklists for critical appraisal. The first of these contains the general questions which can be asked of any study using a quantitative methodology. The succeeding five chapters review in turn the questions which are specific for each quantitative method. For convenience each of these five chapters concludes with a combined list of general and specific questions.
The book has been written to be simple and quick to use. Technical terms are avoided where possible, and the assessment criteria are explained but not justified. A larger and less accessible text would have been needed to give a proper rationale for each the checklists. To keep this a pocket guide, it was also decided to omit evaluations of other topics such as qualitative methods, health economics, clinical audit, decision analysis, and screening tests. An argument could be made for the inclusion of each, but to include them all would nearly double the size of the book. I hope the checklists prove useful.
Preface to the Second Edition
Several developments have highlighted the need for a second edition of this book. Recent work, particularly from the new discipline of meta‐research, has provided important evidence for critical appraisal. By examining and comparing large numbers of studies, this research has clarified the nature of and impact of many sources of bias. A separate development is the recognition that critical appraisal should distinguish between the risk of bias and the value of the findings to individuals, health care systems, and the wider society. Critical appraisal checklists should provide separate sets of questions for the two issues. Finally, many years of teaching critical appraisal skills have provided the author with an understanding of the difficulties that students and health professionals encounter when evaluating papers. These developments have led to improvements in the guidance given in this book.
This new edition follows the format and the spirit of the first: it is written to be easy to use and, where possible, technical terms are avoided. However, substantial modifications have been made. A new Introduction clarifies the aims of critical appraisal. The second chapter, entitled ‘Do Not Read the Paper’, is also new; it provides a simple method for eliciting the information needed for critical appraisal from published studies. This is supported by Chapter 5, ‘The In‐Depth Interrogation’, which is a much‐amended version of the original ‘Standard Appraisal Questions’. In addition, Chapter 4 on ‘Interpreting the Results’ has been updated in line with current views on the nature of statistical significance and the interpretation of confidence intervals.
All of the chapters that provide checklists for critical appraisal of specific research designs have been revised and updated, particularly Chapter