Interpreting Evidence

This book explains the correct logical approach to analysis of forensic scientific evidence. The focus is on general methods of analysis applicable to all forms of evidence. It starts by explaining the general principles and then applies them to issues in DNA and other important forms of scientific evidence as examples. Like the first edition, the book analyses real legal cases and judgments rather than hypothetical examples and shows how the problems perceived in those cases would have been solved by a correct logical approach. The book is written to be understood both by forensic scientists preparing their evidence and by lawyers and judges who have to deal with it. The analysis is tied back both to basic scientific principles and to the principles of the law of evidence. This book will also be essential reading for law students taking evidence or forensic science papers and science students studying the application of their scientific specialisation to forensic questions.

Autorentext

Bernard Robertson, Barrister, Inner Temple and New Zealand
Bernard Robertson is a graduate of Oxford, of the LSE, and of the National Police Staff College, Bramshill as well as being a Barrister of the Inner Temple and of New Zealand. After ten years in the Metropolitan Police, Bernard emigrated to New Zealand and taught the law of evidence at undergraduate and postgraduate levels. He and Professor Vignaux have written numerous papers on Bayesian analysis of scientific evidence and of evidence and court decision making in general. He has also been editor of The New Zealand Law Journal and of The New Zealand Law Reports, ensuring that he has kept in touch with a wide range of legal issues, including civil litigation. G. A.Vignaux, Emeritus Professor,?Victoria University, New Zealand
G A (Tony) Vignaux (retired) was a physicist and an Operations Research worker, and latterly a Professor of Operations Research at Victoria University. Prior to starting work on legal questions he published on the use of Bayesian methods in physics. With Bernard Robertson he has been invited to address conferences and has been consulted on several legal cases and by enquiries into miscarriage of justice. He has participated in teaching evidence and forensic science to law students at postgraduate level. **Charles Berger, Principal Scientist,?Netherlands Forensic Institute,?The NetherlandsPreface to the First Edition xi

Preface to the Second Edition xv

1. Introduction 1

1.1 Three 'principles' 1

1.2 Dreyfus, Bertillon, and Poincaré 3

1.3 Requirements for Forensic Scientific Evidence 5

1.3.1 Reliability 6

1.4 What We Will Cover 6

2. Interpreting Scientific Evidence 9

2.1 Relevance and Probative Value 9

2.1.1 Ideal and Useless Evidence 10

2.1.2 Typical Evidence 11

2.1.3 An Aside on Probability and Odds 11

2.1.4 A Breath-Testing Device 13

2.2 The Likelihood Ratio and Bayes' Theorem 14

2.2.1 The Likelihood Ratio 14

2.2.2 Bayes' Theorem 15

2.2.3 The Effect of Prior Odds 16

2.2.4 An HIV Test 16

2.2.5 Transposing the Conditional 17

2.2.6 Giving Evidence 18

2.3 Admissibility and Relevance 19

2.3.1 Prejudging the Case? 20

2.4 Case Studies 21

2.4.1 A Useful Presentation of DNA Evidence 21

2.4.2 The Shoe Mark at the Murder Scene 22

2.4.3 The Probability of Paternity 23

2.4.4 Child Sexual Abuse 26

2.5 Summary 27

3. The Alternative Hypothesis 29

3.1 Some Symbols 29

3.1.1 Hypotheses 29

3.1.2 Evidence 30

3.1.3 Probability 30

3.2 Which Alternative Hypothesis? 30

3.2.1 Probative Value and the Alternative Hypothesis 30

3.2.2 Selecting the Appropriate Alternative Hypotheses 31

3.2.3 Example 32

3.3 Exclusive, Exhaustive, and Multiple Hypotheses 33

3.3.1 Exclusiveness 33

3.3.2 Exhaustiveness 34

3.3.3 Multiple Hypotheses 35

3.4 Immigration and Paternity Cases 35

3.4.1 No Alternative Father 36

3.4.2 A Named Alternative Father 36

3.4.3 An Older Example 37

3.5 'It Was My Brother' 38

3.6 Traces at the Scene and Traces on the Suspect 39

3.6.1 Traces at the Scene 39

3.6.2 Traces on the Accused 39

3.6.3 The Accused's Race 40

3.7 Hypothetical Questions 40

3.8 Pre-Trial Conferences and Defence Notice 42

3.9 Case Studies 43

3.9.1 Alternative Hypotheses in Cases of Child Sexual Abuse 43

3.9.2 The Shoe Mark Case Again 43

3.9.3 Sally Clark 44

3.10 Summary 45

4. What Questions Can the Expert Deal With? 47

4.1 The Hierarchy of Propositions 47

4.2 The Ultimate Issue Rule 50

4.2.1 Rationale 51

4.2.2 Experts Must Not Give Evidence on Legal Concepts 51

4.2.3 The Rule and Logical Inference 52

4.2.4 The Ultimate Issue Rule Is Correct 53

4.3 Summary 54

5. Explaining the Strength of Evidence 55

5.1 Explaining the Likelihood Ratio 56

5.1.1 Sensitivity Tables 57

5.2 The Weight of Evidence 57

5.3 Words Instead of Numbers? 58

5.3.1 Standardising Word Meanings 59

5.3.2 The Inconsistent Meanings of 'Consistent' 60

5.3.3 'Could Have' and 'Could Have Not' 61

5.3.4 There's Nothing Special about Being 'Unique' 61

5.3.5 'Reliability' 62

5.3.6 Other Words to Avoid 63

5.4 Dealing with Wrongly Expressed Evidence 63

5.5 Case Studies 64

5.5.1 Shoe Marks 64

5.5.2 Stomach Contents 66

5.5.3 Hair Growth 66

5.6 Summary 67

6. The Case as a Whole 69

6.1 Combining Evidence 69

6.1.1 Dependent and Independent Evidence 70

6.1.2 Conditional Independence 71

6.1.3 Combining Dependent Evidence 72

6.2 Can Combined Weak Evidence Be Stronger Than Its Components? 72

6.3 The Standard of Proof and the Cost of Errors 74

6.3.1 Civil Cases 75

6.3.2 Criminal Cases 75

6.3.3 Child Sex-Abuse Cases 75 6.3.4 Is a Quantifiable...