Medical Decision Making

Foreword xi

Preface xiii

1 Introduction 1

1.1 How may I be thorough yet efficient when considering the possible causes of my patient’s problems? 1

1.2 How do I characterize the information I have gathered during the medical interview and physical examination? 1

1.3 How do I interpret new diagnostic information? 3

1.4 How do I select the appropriate diagnostic test? 4

1.5 How do I choose among several risky treatment alternatives? 4

2 Differential diagnosis 5

2.1 An introduction 5

2.2 How clinicians make a diagnosis 5

2.3 The principles of hypothesis- driven differential diagnosis 8

2.4 An extended example 14

Bibliography 16

3 Probability: quantifying uncertainty 18

3.1 Uncertainty and probability in medicine 18

3.2 How to determine a probability 21

3.3 Sources of error in using personal experience to estimate the probability 23

3.4 The role of empirical evidence in quantifying uncertainty 30

3.5 Limitations of published studies of disease prevalence 35

3.6 Taking the special characteristics of the patient into account when determining probabilities 36

Bibliography 37

4 Interpreting new information: Bayes’ theorem 38

4.1 Introduction 38

4.2 Conditional probability defined 40

4.3 Bayes’ theorem 41

4.4 The odds ratio form of Bayes’ theorem 45

4.5 Lessons to be learned from using Bayes’ theorem 50

4.6 The assumptions of Bayes’ theorem 52

4.7 Using Bayes’ theorem to interpret a sequence of tests 54

4.8 Using Bayes’ theorem when many diseases are under consideration 55

Bibliography 57

5 Measuring the accuracy of clinical findings 58

5.1 A language for describing test results 58

5.2 The measurement of diagnostic test performance 62

5.3 How to measure diagnostic test performance: a hypothetical example 67

5.4 Pitfalls of predictive value 69

5.5 How to perform a high quality study of diagnostic test performance 70

5.6 Spectrum bias in the measurement of test performance 74

5.7 When to be concerned about inaccurate measures of test performance 79

5.8 Test results as a continuous variable: the ROC curve 81

5.9 Combining data from studies of test performance: the systematic review and meta- analysis 87

A.5.1 Appendix: derivation of the method for using an ROC curve to choose the definition of an abnormal test result 89

Bibliography 91

6 Decision trees – representing the structure of a decision problem 93

6.1 Introduction 93

6.2 Key concepts and terminology 93

6.3 Constructing the decision tree for a hypothetical decision problem 96

6.4 Constructing the decision tree for a medical decision problem 103

Epilogue 112

Bibliography 112

7 Decision tree analysis 113

7.1 Introduction 113

7.2 Folding- back operation 114

7.3 Sensitivity analysis 126

Epilogue 133

Bibliography 133

8 Outcome utility – representing risk attitudes 134

8.1 Introduction 134

8.2 What are risk attitudes? 135

8.3 Demonstration of risk attitudes in a medical context 136

8.4 General observations about outcome utilities 147

8.5 Determining outcome utilities – underlying concepts 151

Epilogue 157

Bibliography 158

9 Outcome utilities – clinical applications 159

9.1 Introduction 159

9.2 A parametric model for outcome utilities 160

9.3 Incorporating risk attitudes into clinical policies 172

9.4 Helping patients communicate their preferences 181

Epilogue 185

A.9.1 Exponential utility model parameter nomogram 186

Bibliography 188

10 Outcome utilities – adjusting for the quality of life 189

10.1 Introduction 189

10.2 Example – why the quality of life matters 190

10.3 Quality- lifetime tradeoff models 193

10.4 Quality- survival tradeoff models 203

10.5 What does it all mean? – an extended example 209

Epilogue 217

Bibliography 217

11 Survival models: representing uncertainty about the length of life 218

11.1 Introduction 218

11.2 Survival model basics 219

11.3 Medical example – survival after breast cancer recurrence 226

11.4 Exponential survival model 228

11.5 Actuarial survival models 232

11.6 Two- part survival models 235

Epilogue 247

Bibliography 247

12 Markov models 248

12.1 Introduction 248

12.2 Markov model basics 249

12.3 Determining transition probabilities 259

12.4 Markov model analysis – an overview 269

Epilogue 277

Bibliography 277

13 Selection and interpretation of diagnostic tests 278

13.1 Introduction 278

13.2 Four principles of decision making 279

13.3 The threshold probability for treatment 281

13.4 Threshold probabilities for testing 288

13.5 Clinical application of the threshold model of decision making 293

13.6 Accounting for the non- diagnostic effects of undergoing a test 296

13.7 Sensitivity analysis 298

13.8 Decision curve analysis 300

Bibliography 302

14 Medical decision analysis in practice: advanced methods 303

14.1 An overview of advanced modeling techniques 303

14.2 Use of medical decision- making concepts to analyze a policy problem: the cost- effectiveness of screening for HIV 305

14.3 Use of medical decision- making concepts to analyze a clinical diagnostic problem: strategies to diagnose tumors in the lung 313

14.4 Calibration and validation of decision models 317

14.5 Use of complex models for individual- patient decision making 319

Bibliography 321

15 Cost- effectiveness analysis 323

15.1 The clinician’s conflicting roles: patient advocate member of society and entrepreneur 323

15.2 Cost- effectiveness analysis: a method for comparing management strategies 325

15.3 Cost–benefit analysis: a method for measuring the net benefit of medical services 330

15.4 Methodological best practices for cost- effectiveness analysis 332

15.5 Reference case for cost- effectiveness analysis 333

15.6 Impact inventory for cataloguing consequences 334

15.7 Measuring the health effects of medical care 334

15.8 Measuring the costs of medical care 335

15.9 Interpretation of cost- effectiveness analysis and use in decision making 337

15.10 Limitations of cost- effectiveness analyses 337

Bibliography 338

Index 340