Screening for Glaucoma using IOP. IOP > 22: Yes (total)

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1 Whose Fault? Error Rates, Diagnosticity, and Overclaiming i In Forensic Science D. Michael Risinger John J. Gibbons Professor of Law Seton Hall University School of Law

2 Si Science or not?

3 Not all, and not only, scientific evidence is reliable Susan Haack

4 There is no silver bullet study that will globally validate an area of practice. It will require lots of subtask studies and a long time.

5 Screening for Glaucoma using IOP True Cases of Glaucoma Yes No IOP > 22: Yes No (total) Sensitivity = 50% (50/100) False Negative=50% Specificity = 95% (1900/2000) False Positive=5%

6 Error comes in many flavors

7

8 Test Positive Test Negative Totals

9 WANDLESS WIZARDS?

10 A place where the science/non- science demarcation is surprisingly unhelpful: Understanding the notion of expertise.

11 Expertise is best understood by functional contrast with the ordinary fact witness.

12 Fact witnesses are interchangeable with jurors except for time and place.

13 Whenever a witness makes assertions that cannot be accounted for by intercheangability, the witness is performing some sort of expert function.

14 Translational expertise is most people s normal model, dealing as it does in conclusions or opinions

15 Translational assertions convert facts equally available to the jury and the expert from a less usable to a more usable form, based on an asserted translation system possessed by the witness but not by the jury.

16 There are many potential species of translational system, the most important of which are: 1. experience based 2. research based

17 In reality, there tends to be an admixture of both in real world applications, but one or the other is usually clearly dominant.

18 In judging reliability of asserted expertise, the questions to be asked are always the same for all forms

19 What is the case specific target issue to which the expertise is directed? What is the case-specific specific claim of expertise? What available information bears on a rational belief warrant in regard to the reliability of this specific claim of expertise? What is the appropriate standard of certainty for such a belief warrant given the kind of case, the issue involved, the distribution ib ti of the burdens of production and persuasion in the case, and the standard of proof involved in regard to the issue upon which the expertise is proffered?

20 Notice that nothing has yet been said about science. Science is only one form of translational system (but an important one)

21 However, when answering question three (about the reasons to believe a claim of expertise), we must decide if we are dealing with science or not, because that shapes how we approach that question.

22 It s not that belief in non-science experienced-based claims is not sometimes warranted, but that they will be warranted (if they are) in a different way than the products of science.

23 So we must now deal with some sort of approach to the demarcation problem.

24 Science is An enterprise committed to cognitive rationality by ideology Not timebound in its search for answers Not (directly) concerned with normative questions beyond cognitive rationality

25 Science is also an enterprise whose individual practitioners may depart substantially from the ideal. a social enterprise dependent d a complex web of checks and balances for its success over time.

26 Fundamental Characteristics Formal Data Reliable Taxonomy Generalizations asserting regularities, based on data Testing of predictions from generalizations by reference to formal data.

27 No Formal Data No Testing of Claims No Science

28 Consider fingerprint identification (And other forensic identification specialties)

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30 Minimum condition of reliability for experience-based expertise: Unambiguous feedback for correct results in normal practice

31 When this condition is not present, only testing of practitioners by the standards of science can supply the appropriate belief warrant.

32 Additional Considerations: Masking The astrology test