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Crash Course Evidence-Based Medicine: Reading and Writing Medical Papers - E-Book

Crash Course Evidence-Based Medicine: Reading and Writing Medical Papers - E-Book

Amit Kaura | Andrew Polmear

(2013)

Additional Information

Abstract

Crash Course – your effective everyday study companion PLUS the perfect antidote for exam stress! Save time and be assured you have all the information you need in one place to excel on your course and achieve exam success.

A winning formula now for over 15 years, each volume has been fine-tuned to make your life easier. Especially written by junior doctors – those who understand what is essential for exam success – with all information thoroughly checked and quality assured by expert Faculty Advisers, the result is a series of books which exactly meets your needs and you know you can trust.

This essential new addition to the series clearly brings together the related disciplines of evidence-based medicine, statistics, critical appraisal and clinical audit – all so central to current study and to modern clinical practice. It starts with the basics that every student needs to know and continues into sufficient detail to satisfy anyone contemplating their own research studies. Excel in Student Selected Component (SSC) assessments and that dreaded evidence-based medicine and statistics exam! Ensure you know how to prepare the highest quality reports and maximize your chances of getting published.

If you are not sure:

  • why you need to know the standard deviation of a sample
  • when to use a case-control study and when a cohort study
  • what to say to your patient who asks about the benefits and harms of a drug
  • how to argue the case for the inclusion of a drug on the hospital formulary
  • how to make audit and quality improvement work for you,

…then this groundbreaking book is for you! Answer these and hundreds of other questions and lay a foundation for your clinical practice that will inform every consultation over a lifetime in medicine.


Table of Contents

Section Title Page Action Price
Front Cover Cover
Crash Course: Evidence-Based Medicine: Reading and Writing Medical Papers iii
Copyright iv
Series editor foreword v
Prefaces vii
Acknowledgements ix
Dedication xi
Contents xiii
Chapter 1: Evidence-based medicine 1
WHAT IS EVIDENCE-BASED MEDICINE? 1
FORMULATING CLINICAL QUESTIONS 1
IDENTIFYING RELEVANT EVIDENCE 2
Sources of information 2
The search strategy 3
Search terms 3
Reviewing the search strategy 4
Expanding your results 4
Limiting your results 4
Documentation of the search strategy 4
CRITICALLY APPRAISING THE EVIDENCE 4
Critical appraisal 4
Hierarchy of evidence 6
ASSESSING THE RESULTS 6
IMPLEMENTING THE RESULTS 6
EVALUATING PERFORMANCE 6
CREATING GUIDELINE RECOMMENDATIONS 7
Chapter 2: Handling data 9
TYPES OF VARIABLES 9
Nominal variable 9
Ordinal variable 9
Interval variable 10
Ratio variable 10
Quantitative (numerical) data 10
Discrete variable 10
Continuous variable 10
Qualitative (categorical) data 10
DISPLAYING THE DISTRIBUTION OF A SINGLE VARIABLE 11
Frequency distributions 11
Displaying frequency distributions 11
Bar chart 11
Pie chart 12
Histogram 13
DISPLAYING THE DISTRIBUTION OF TWO VARIABLES 13
Numerical versus numerical variables 14
Categorical versus categorical variables 14
Numerical versus categorical variables 14
Box and whisker plot 14
Bar chart 15
Dot plot 15
DESCRIBING THE FREQUENCY DISTRIBUTION: CENTRAL TENDENCY 15
The arithmetic mean 15
The mode 16
The median 16
DESCRIBING THE FREQUENCY DISTRIBUTION: VARIABILITY 16
The range 17
The inter-quartile range 17
Percentiles 17
The standard deviation 17
Population standard deviation 17
Sample standard deviation 17
THEORETICAL DISTRIBUTIONS 18
Probability distributions 18
The rules of probability 18
Mutually exclusive events 18
Independent events 18
Defining probability distributions 18
Continuous probability distributions 18
The normal (Gaussian) distribution 19
Reference range 19
`Standard´ normal distribution 20
Other continuous probability distributions 20
Discrete probability distributions 20
Skewed distributions 20
Positively skewed distributions 20
Negatively skewed distributions 20
TRANSFORMATIONS 20
The logarithmic transformation 21
The geometric mean 21
Calculating the anti-log 22
The square transformation 22
CHOOSING THE CORRECT SUMMARY MEASURE 22
Chapter 3: Investigating hypotheses 23
HYPOTHESIS TESTING 23
The null and alternative hypotheses 23
CHOOSING A SAMPLE 23
Accuracy versus precision 24
Accuracy 24
Precision 24
EXTRAPOLATING FROM ` SAMPLE´ TO `POPULATION´ 24
Standard error of the mean 24
Standard error versus standard deviation 25
Confidence interval for the mean 25
Confidence interval versus reference range 26
Confidence interval for a proportion 26
The effect of simvastatin on stroke risk 27
What is a large sample? 28
COMPARING MEANS AND PROPORTIONS: CONFIDENCE INTERVALS 28
Confidence interval for the difference between two independent means 28
Confidence interval for the difference between paired means 29
Confidence interval for the difference between two independent proportions 30
Plotting error bars 30
THE P-VALUE 31
Statistical hypothesis testing 31
Calculating the P-value 31
One-tail versus two-tail P-values 32
STATISTICAL SIGNIFICANCE AND CLINICAL SIGNIFICANCE 32
Interpreting small P-values (P<0.05) 32
Chapter 4: Systematic review and meta-analysis 41
WHY DO WE NEED SYSTEMATIC REVIEWS? 41
Rationale for systematic reviews 41
Traditional reviews 41
Principles and conduct of systematic reviews 42
Developing a systematic review: steps 1-3 42
EVIDENCE SYNTHESIS 42
META-ANALYSIS 42
Why do a meta-analysis? 42
Combining estimates in a meta-analysis 42
Heterogeneity 43
Tests for evidence of heterogeneity 43
Estimating the degree of heterogeneity 43
Investigating sources of heterogeneity 43
Calculating the pooled estimate in the absence of heterogeneity 43
Fixed-effects meta-analysis 43
Dealing with heterogeneity 44
Not performing a meta-analysis 44
Random-effects meta-analysis 44
Subgroup analysis 44
Fixed-effects versus random-effects meta-analysis 45
Sensitivity analysis 45
PRESENTING META-ANALYSES 45
EVALUATING META-ANALYSES 45
Interpreting the results 45
Bias in meta-analyses 46
Production of evidence 46
Dissemination of evidence 46
Publication bias 47
Detecting publication bias 47
Other causes of funnel plot asymmetry 47
Preventing publication bias 47
ADVANTAGES AND DISADVANTAGES 48
KEY EXAMPLE OF A META-ANALYSIS 48
REPORTING A SYSTEMATIC REVIEW 49
Chapter 5: Research design 53
OBTAINING DATA 53
INTERVENTIONAL STUDIES 53
OBSERVATIONAL STUDIES 54
CLINICAL TRIALS 55
Types of clinical trials 55
Clinical trial phases 56
Pre-clinical trials 56
Phase I trials 56
Phase II trials 56
Phase III trials 56
Phase IV trials 56
BRADFORD-HILL CRITERIA FOR CAUSATION 57
Strength of association 58
Consistency 58
Specificity 58
Temporal sequence 58
Biological gradient (dose-response) 58
Biological plausibility 58
Coherence 58
Reversibility (experimental evidence) 59
Analogy 59
CHOOSING THE RIGHT STUDY DESIGN 59
Using the hierarchy of evidence 59
WRITING UP A RESEARCH STUDY 59
Title 60
Abstract 60
Introduction 61
Methods 61
Results 62
Discussion 62
References 62
Journal articles 63
Books 63
Chapters in books 63
Websites 63
Dissertations and theses 63
Verbal materials: interviews 63
Unpublished material: lecture notes 63
Chapter 6: Randomised controlled trials 65
WHY CHOOSE AN INTERVENTIONAL STUDY DESIGN? 65
PARALLEL RANDOMISED CONTROLLED TRIAL 65
Study design 65
Inclusion/exclusion criteria 66
Choice of comparator 67
Sample size 67
The outcome measure 67
Ethical issues 68
Clinical equipoise 68
Informed consent 68
Randomisation 69
Methods of randomisation 69
Simple randomisation 69
Block randomisation 69
Stratified randomisation 69
Minimisation 69
Allocation sequence concealment 70
Blinding 70
CONFOUNDING, CAUSALITY AND BIAS 70
Confounding 70
Causality 71
Bias 71
Selection bias 71
Bias associated with randomisation: random sequence generation bias and allocation of intervention bias 71
Bias during study implementation: contamination bias 72
Bias during study implementation: loss-to-follow-up bias 72
Measurement bias 72
Random misclassification bias 72
Non-random misclassification bias 73
Performance bias 73
Detection bias 73
Recall bias 73
Interviewer bias 73
INTERPRETING THE RESULTS 73
Interim analysis 74
Adjusting for confounders 74
Intention to treat analysis 74
Efficacy versus effectiveness 75
Sensitivity analysis 75
Subgroup analysis 75
Numbers needed to treat for benefit and harm 75
NNTB example 75
NNTH example 76
TYPES OF RANDOMISED CONTROLLED TRIALS 76
Two or more parallel groups 76
Cross-over trial 76
Factorial trial 77
Cluster trial 77
Superiority versus equivalence trials 77
Superiority trial 77
Equivalence trial 77
ADVANTAGES AND DISADVANTAGES 78
KEY EXAMPLE OF A RANDOMISED CONTROLLED TRIAL 78
REPORTING A RANDOMISED CONTROLLED TRIAL 78
Chapter 7: Cohort studies 83
STUDY DESIGN 83
INTERPRETING THE RESULTS 84
Risk 84
Risk ratios 84
Confidence interval for a risk ratio 84
Risk difference 86
Risk ratio versus risk difference 86
CONFOUNDING, CAUSALITY AND BIAS 86
Confounding 86
Causality 87
Bias 87
Selection bias 88
Bias during study implementation: loss-to-follow-up bias 88
Participation bias: non-response bias 88
Eligible population inappropriately defined: healthy worker effect bias 88
Ascertainment bias: healthcare access bias 89
Measurement bias 89
Random misclassification bias 89
Non-random misclassification bias 89
Performance bias: follow-up bias 89
Detection bias: diagnostic suspicion bias 89
Recall bias: rumination bias and exposure suspicion bias 89
Interviewer bias: observer expectation bias and apprehension bias 90
ADVANTAGES AND DISADVANTAGES 90
KEY EXAMPLE OF A COHORT STUDY 90
Chapter 8: Case-control studies 93
STUDY DESIGN 93
Case definition 93
Case selection 94
Control selection 95
Matching 95
Measuring exposure status 95
INTERPRETING THE RESULTS 96
Odds and odds ratio 97
Calculating the odds ratio 97
Interpreting the odds ratio 97
Confidence interval for an odds ratio 97
Odds ratio versus risk ratio 97
CONFOUNDING, CAUSALITY AND BIAS 99
Confounding 99
Causality 99
Bias 99
Selection bias 99
Eligible population inappropriately defined: hospital admission rate bias 99
Eligible population inappropriately defined: exclusion bias and inclusion bias 100
Eligible population inappropriately defined: overmatching bias 100
Participation bias: non-response bias 101
Detection bias 101
Ascertainment bias: incidence-prevalence bias 101
Ascertainment bias: healthcare access bias 102
Ascertainment bias: migration bias 102
Measurement bias 102
Random misclassification bias 102
Non-random misclassification bias 102
ADVANTAGES AND DISADVANTAGES 102
KEY EXAMPLE OF A CASE- CONTROL STUDY 102
Chapter 9: Measures of disease occurrence and cross-sectional studies 105
MEASURES OF DISEASE OCCURRENCE 105
Prevalence 105
Incidence risk 105
Incidence rate 106
Calculating person-time 106
When does a person become a case? 107
Prevalence versus incidence 108
STUDY DESIGN 109
Descriptive cross-sectional studies 109
Analytical cross-sectional studies 109
Selecting a representative sample 110
Repeated cross-sectional studies 110
INTERPRETING THE RESULTS 110
Prevalence 110
Prevalence odds ratio 111
Prevalence ratio 111
Prevalence odds ratio versus prevalence ratio 111
CONFOUNDING, CAUSALITY AND BIAS 112
Confounding 112
Causality 112
Bias 112
Selection bias 112
Participation bias: non-response bias 113
Ascertainment bias: incidence-prevalence bias 113
Ascertainment bias: healthcare access bias 113
Ascertainment bias: migration bias 113
Measurement bias 113
Random misclassification bias 114
Non-random misclassification bias 114
ADVANTAGES AND DISADVANTAGES 114
KEY EXAMPLE OF A CROSS-SECTIONAL STUDY 114
Chapter 10: Ecological studies 117
STUDY DESIGN 117
Levels of measurement 117
Levels of inferences 117
Types of ecological studies 118
Time trend studies 118
Geographical studies 118
Mixed design 118
Data collection 118
INTERPRETING THE RESULTS 118
Scatter plots and correlation coefficients 119
Regression analysis 119
Discussing the findings of a mixed design study 119
SOURCES OF ERROR IN ECOLOGICAL STUDIES 119
Ecological fallacy 119
Within-group bias 121
Confounding by group 121
Effect modification by group 121
Confounders and modifiers 122
Causality 122
ADVANTAGES AND DISADVANTAGES 122
Individual-level studies versus group-level studies 122
Design limitations of individual-level studies 122
Measurement limitations of individual-level studies 123
KEY EXAMPLE OF AN ECOLOGICAL STUDY 123
Relationship between socioeconomic status and mortality after an acute myocardial infarction 123
Chapter 11: Case report and case series 125
BACKGROUND 125
CONDUCTING A CASE REPORT 125
Preparation 125
Structuring a medical case report 125
Abstract 126
Introduction 126
Case presentation 126
Discussion 126
Conclusion 126
References 126
CONDUCTING A CASE SERIES 127
CRITICAL APPRAISAL OF A CASE SERIES 127
ADVANTAGES AND DISADVANTAGES 127
KEY EXAMPLES OF CASE REPORTS 127
The first cardiac transplantation 127
Multiple myeloma 128
KEY EXAMPLE OF A CASE SERIES 128
Thalidomide and congenital abnormalities 128
Chapter 12: Qualitative research 129
STUDY DESIGN 129
What is qualitative research? 129
Qualitative versus quantitative research methods 129
Methods of data collection 130
Participant observation 130
In-depth interviews 130
Focus groups 131
Sampling 131
Purposive sampling 131
Quota sampling 131
Snowball sampling 131
Maximum variation sampling 132
Negative sampling 132
ORGANISING AND ANALYSING THE DATA 132
Organising the data 132
Analysing the data 132
VALIDITY, RELIABILITY AND TRANSFERABILITY 132
Validity 132
Reliability 133
Transferability 133
ADVANTAGES AND DISADVANTAGES 133
KEY EXAMPLE OF QUALITATIVE RESEARCH 133
Chapter 13: Confounding 135
WHAT IS CONFOUNDING? 135
ASSESSING FOR POTENTIAL CONFOUNDING FACTORS 135
Association with exposure 136
The confounder causes the exposure 136
The confounder is a result from the exposure 136
The confounder is related to the exposure with a non-causal association 136
Association with disease 137
CONTROLLING FOR CONFOUNDING FACTORS 137
Design stage 137
Randomisation 137
Restriction 137
Matching 137
Analysis stage 138
Stratified analysis 138
Mathematical modelling 138
REPORTING AND INTERPRETING THE RESULTS 138
KEY EXAMPLE OF STUDY CONFOUNDING 139
Chapter 14: Screening, diagnosis and prognosis 141
SCREENING, DIAGNOSIS AND PROGNOSIS 141
DIAGNOSTIC TESTS 141
EVALUATING THE PERFORMANCE OF A DIAGNOSTIC TEST 142
Sensitivity and specificity 142
Using sensitivity and specificity to make clinical decisions 144
False positives and false negatives 144
Positive and negative predictive values 144
THE DIAGNOSTIC PROCESS 145
Pre-test probability 145
Post-test probability 145
Estimating the post-test probability using predictive values 145
Estimating the post-test probability using likelihood ratios 147
EXAMPLE OF A DIAGNOSTIC TEST USING PREDICTIVE VALUES 148
Case 1: Low pre-test probability/low prevalence 149
Case 2: Equivocal pre-test probability/high prevalence 150
Case 3: High pre-test probability/high prevalence 150
BIAS IN DIAGNOSTIC STUDIES 150
Spectrum bias 150
Verification bias 150
Partial verification bias 151
Differential verification bias 151
Loss-to-follow-up bias 151
Reporting bias 152
SCREENING TESTS 152
Diagnostic tests versus screening tests 152
Screening programmes 152
Screening programme evaluation 153
Selection bias 153
Length time bias 153
Lead-time bias 154
EXAMPLE OF A SCREENING TEST USING LIKELIHOOD RATIOS 155
PROGNOSTIC TESTS 155
Prognostic studies 156
Measuring prognosis 157
Morbidity 157
Mortality 157
Chapter 15: Statistical techniques 159
CHOOSING APPROPRIATE STATISTICAL TESTS 159
Data analysis goal 159
Type of variable 159
Data distribution 160
Gaussian versus non-Gaussian distributions 160
When to choose a non-parametric test 160
Sample size matters 160
COMPARISON OF ONE GROUP TO A HYPOTHETICAL VALUE 161
COMPARISON OF TWO GROUPS 161
Chi-squared test and Fisher's exact test 163
COMPARISON OF THREE OR MORE GROUPS 163
MEASURES OF ASSOCIATION 163
Chapter 16: Clinical audit 167
INTRODUCTION TO CLINICAL AUDIT 167
Clinical governance 167
What is clinical audit? 167
Clinical audit versus clinical research 167
Similarities between audit and research 167
Differences between audit and research 168
PLANNING THE AUDIT 169
Identifying a topic 169
Sources of inspiration 169
Formulating the audit question 169
CHOOSING THE STANDARDS 169
AUDIT PROTOCOL 170
DEFINING THE SAMPLE 170
DATA COLLECTION 171
ANALYSING THE DATA 171
EVALUATING THE FINDINGS 171
Standards achieved 171
Standards not achieved 172
IMPLEMENTING CHANGE 172
EXAMPLE OF A CLINICAL AUDIT 172
Audit question 172
The standards 172
The sample 173
Data collection 173
Analysing data 173
Evaluating performance 173
Implementing change 174
Chapter 17: Quality improvement 175
QUALITY IMPROVEMENT VERSUS AUDIT 175
THE MODEL FOR QUALITY IMPROVEMENT 175
THE AIM STATEMENT 175
Writing the statement 175
Example 176
Statement 176
Dimensions for improvement 176
MEASURES FOR IMPROVEMENT 177
Types of measures 177
Outcome measures 177
Process measures 177
Balancing measures 177
Chapter 18: Economic evaluation 183
WHAT IS HEALTH ECONOMICS? 183
Background 183
Efficiency 183
Technical efficiency 183
Productive efficiency 183
Allocative efficiency 183
Opportunity costs 184
Economic evaluation 184
ECONOMIC QUESTION AND STUDY DESIGN 185
Economic question 185
Costs 185
Study design 185
COST-MINIMISATION ANALYSIS 185
Clinical equivalence 186
What is clinical equivalence? 186
Demonstrating clinical equivalence 186
Superiority trials 186
Equivalence trials 186
Non-inferiority trials 186
COST-UTILITY ANALYSIS 187
Health utilities 188
Direct measurement of utilities 188
Visual analogue scale 188
Time trade-off 188
Standard gamble 189
Which valuation method is best? 189
Public versus patients 189
Indirect measurement of utilities 190
Quality-adjusted life years (QALYs) 190
Example 1: QALY - intervention A versus intervention B (Fig.18.8) 190
Example 2: QALY - intervention C versus intervention D (Fig.18.9) 190
Implementing QALYs 190
The net monetary benefit statistic 192
Advantages and disadvantages of a cost-utility analysis 192
COST-EFFECTIVENESS ANALYSIS 193
Independent interventions 193
Mutually exclusive interventions 193
The cost-effectiveness plane 195
Advantages and disadvantages of a cost-effectiveness analysis 195
COST-BENEFIT ANALYSIS 195
SENSITIVITY ANALYSIS 196
One-way sensitivity analysis 196
Multi-way sensitivity analysis 196
Probabilistic sensitivity analysis 196
Chapter 19: Critical appraisal checklists 199
CRITICAL APPRAISAL 199
Clinical question 199
Study design 199
Ethical issues 199
Study population 199
Study methods 200
Data analysis 200
Confounding and bias 200
Discussion 200
SYSTEMATIC REVIEWS AND META-ANALYSES 202
RANDOMISED CONTROLLED TRIALS 202
DIAGNOSTIC STUDIES 203
QUALITATIVE STUDIES 204
Chapter 20: Crash course in statistical formulae 205
DESCRIBING THE FREQUENCY DISTRIBUTION 205
EXTRAPOLATING FROM `SAMPLE´ TO `POPULATION´ 205
STUDY ANALYSIS 205
TEST PERFORMANCE 205
ECONOMIC EVALUATION 205
Chapter 21: Careers in academic medicine 209
CAREER PATHWAY 209
Academic Foundation Programme (AFP) 209
Academic clinical fellowship (ACF) 209
Academic clinical lectureship (ACL) 209
GETTING INVOLVED 210
What is my career path to date? 210
What inspired me to embark upon an academic career? 210
What do I like about being a clinical academic? 211
What challenges have I faced? 211
Advice for someone considering a career in academic medicine 211
PROS AND CONS 211
References 213
Chapter 3 213
Chapter 4 213
Chapter 6 213
Chapter 7 213
Chapter 8 213
Chapter 9 213
Chapter 10 213
Chapter 11 213
Chapter 12 213
Chapter 13 214
Chapter 14 214
Self-assessment 215
Single best answer (SBA) questions 217
Extended matching questions (EMQs) 225
SBA answers 233
EMQ answers 239
Further reading 245
Chapter 1 245
Chapter 2 245
Chapter 3 245
Chapter 4 245
Chapter 5 245
Chapter 6 245
Chapter 7 245
Chapter 8 246
Chapter 9 246
Chapter 10 246
Chapter 11 246
Chapter 12 246
Chapter 13 246
Chapter 14 246
Chapter 15 246
Chapter 16 246
Chapter 17 246
Chapter 18 246
Chapter 19 247
Chapter 21 247
Glossary 249
Index 253