Foreword viii Preface ix Acknowledgements xii 1 Evidence-based dentistry: what it is and how to practice it 1 What is evidence-based dentistry? 1 Why do we need evidence-based dentistry? 2 How to practice evidence-based dentistry 3 2 Counting people: understanding percentages and proportions 10 What is the aim of the study? 10 How was the study conducted? 11 What are the main results? 12 The implications of conducting a study based on a sample of people 15 How good is the evidence? 19 What does the study contribute to dental practice? 23 3 Taking measurements on people 31 What is the aim of the study? 31 How was the study conducted? 32 What are the main results? 35 Normal distribution 35 Interpreting the results from non-symmetric data 40 4 Comparing groups of people and examining associations 44 Comparing two percentages (or proportions) 44 Comparing two means 51 Examining associations 55 5 Assessing the effectiveness of treatments 68 Main design elements of randomised clinical trials 69 A clinical trial based on counting people 71 A clinical trial based on taking measurements on people 89 Appendix I. Guidelines for the appraisal of a clinical trial 99 6 Determining risk factors for and causes of disease 115 Association, causality and confounding 116 Cohort studies 119 An example of a cohort study 121 Case-control studies 131 An example of a case-control study 132 Appendix I. Guidelines for the appraisal of an observational study 141 Appendix II. Calculation of odds, risk, odds ratio and relative risk 143 7 Detecting disease 154 Conditions for a worthwhile screening programme 156 8 Study design issues 172 Types of study 172 Selecting the sample 172 Sample size 173 More observational studies 177 Bias 178 Confounding 180 More on clinical trials 182 What is the strength of evidence for causality from different study types? 183 9 Reviewing all the evidence 186 Searching for information 186 Conflicts of interests in published research 188 Systematic reviews 189 10 Summary of statistical concepts 205 Suggested answers 209 Further reading 219 Index 222.