ood Forensi S ien e

1. ood Forensi S ien e John Buckleton

2. Good Forensic Science A view from the bottom by John Buckleton With thanks to my great mentors Ian Evett and Bruce Weir John Buckleton

3. What can the 80’s and 90’s teach us? • In most cases the interpretation “arguments” were never settled. • They were superseded by technology or they remain • Product rule or not? • The place of independence testing? • Relatives? • Two stain at a scene John Buckleton

4. Why we have been unable, by science alone, to settle the interpretation matters of our day? John Buckleton

5. WHAT IS THE QUESTION? John Buckleton

6. “The germane question is: What is the frequency in the database?” • Budowle B. National Forensic Science Training Centre, • Florida, 1996. John Buckleton

7. First ‘germane’. Oxford gives this as: “Relevant, pertinent to the matter or subject”. • It must certainly be agreed that it is important to ask relevant questions so it certainly seems important to define the germane question. John Buckleton

8. Since this question is germane let us try answering it. • Imagine that we have a 13 locus STR match. • search the database of say 200 persons (a plausible size in the USA) for this profile • almost certainly do not find it? • We can now answer the germane question: John Buckleton

9. “What is the frequency in the database?” “Hmmmm. What shall I do with that information?” The frequency in the database is zero John Buckleton

10. The question, if taken literally, is not much use. • If it cannot be taken literally then can the question be improved? • Perhaps the author didn’t mean database • perhaps he meant population. John Buckleton

11. “What I meant was, the germane question is: What is the frequency in the population?” John Buckleton

12. Here the last word has been changed from database (where the frequency is zero) to population? • This seems quite a lot better. • Armed with this, we approach our database of 200 persons and attempt to answer this “germane” question. • What can we do next? John Buckleton

13. What has happened is that we have changed from database • completely characterized • we can count any frequencies • to talking about a “population” • There is uncertainty about the population. • do not KNOW the frequency of the genotype in the population. • may even have difficulty defining the population. John Buckleton

14. Accept that we are now estimating something • There is uncertainty in the estimation process. • We will need, at least: • A population genetic model. • A statistical theory to assess sampling error. • Estimation of something very small is difficult. John Buckleton

15. “What I really meant was, What is the product rule estimate from this database?” It would be sad if the audience’s positive reaction was because they liked the simplicity of this statement or that they knew how to do it or that they didn’t have to learn anything new. John Buckleton

16. Evett IW. (1983) What is the probability that this blood came from that person: A meaningful question? J Forensic Sci Soc 23:35-59. “What is the probability that this blood came from that person?” John Buckleton

17. The second was set up deliberately to answer a question of relevance to the court. • The first did not start from this formalized line of thinking. • The second is the more “germane” question. John Buckleton

18. This is the lesson that can be taken from the analysis of this question: • If you don’t have some firm principles on which to base your forensic thinking you can be left relying on your intuition. • Sometimes this will be adequate but it will seldom stand up in comparison to a professional, scholarly and logical approach. John Buckleton

19. Uniqueness? John Buckleton

20. Your honor, this profile is unique, to a reasonable degree of scientific certainty. “That sounds very objective. I like that. What do you mean when you say the profile is unique?” John Buckleton

21. I mean it has met objective criteria developed by my laboratory. “What are these criteria?” John Buckleton

22. We defined a reasonable degree of scientific certainty by setting an acceptable error rate for this decision. “Ouch. That’s really my job” John Buckleton

23. We ignored all issues regarding relatedness. “Why?” John Buckleton

24. We assumed a population genetic model called the product rule. “Ouch. How can you be sure that is correct?” John Buckleton

25. We assumed a population genetic model called the product rule. “Would it be better to accept that there is some uncertainty in the model?” John Buckleton

26. I’ve done lots of data analysis and I think it is OK or near enough. “This sounds more like an opinion than an objective criterion.” John Buckleton

27. This is a fallacy. Independence testing cannot prove the product rule Independence testing shows that I’m right. John Buckleton

28. They are also consistent with minor subdivision Yes, but the data are consistent with expectation for independence.. John Buckleton

29. Caucasian Eastern PolynesianWestern Polynesian • Pr Pr Pr • VWA 0.698 0.297 0.195 • THO1 0.395 0.755 0.266 • D8 0.706 0.912 0.105 • FGA 0.359 0.644 0.913 • D21 0.714 0.752 0.709 • D18 0.632 0.215 0.129 • VWA/THO1 0.505 0.131 0.656 • VWA/D8 0.482 0.232 0.424 • VWA/FGA 0.112 0.506 0.893 • VWA/D21 0.704 0.058 0.949 • VWA/D18 0.283 0.715 0.751 • THO1/D8 0.111 0.982 0.299 • THO1/FGA 0.535 0.964 0.324 • THO1/D21 0.338 0.711 0.416 • THO1/D18 0.057 0.241 0.025 • D8/FGA 0.117 0.938 0.858 • D8/D21 0.240 0.563 0.456 • D8/D18 0.320 0.106 0.210 • FGA/D21 0.209 0.668 0.901 • FGA/D18 0.0280.0150.400 • D21/D18 0.115 0.229 0.636 John Buckleton

30. John Buckleton

31. Post hoc rationalization • Most unwise • Budolwe et al. • testing the FBI’s HBGG locus, appear to have combined the A and C alleles. • There is a significant departure from independence if the alleles are not combined, caused largely by a single CC homozygote. John Buckleton

32. Post hoc rationalization • Result does not appear in the paper • Budowle et al. conclude that the data are “consistent” with Hardy-Weinberg expectations • This is an unreasonable statement considering the (presumably) post hoc combination of two alleles. John Buckleton

33. We BELIEVE • That the effects of subdivision are relatively minor • They do, however, add across loci John Buckleton

34. OK so it’s minor so we can safely ignore it. It has no “forensic significance.” “I won’t dare ask what Forensic significance means. Would it not be more scientific to quantify the effect?” John Buckleton

35. Well that makes things quite complex. “It seems to me more scientific . It is also a principle of law that doubt should be given to the accused.” John Buckleton

36. Why are many countries dropping their point count rules in fingerprints and accepting that a statement of common source in fingerprints is an expert opinion? John Buckleton

37. USA v Byron C Mitchell Individualisation ..can result from comparisons.… containing a sufficient quality .. and quantity of unique friction ridge detail This sounds like expert opinion evidence, especially words like “sufficient quality” John Buckleton

38. Has the SCIENTIFIC basis for statements of common source in DNA been really thought through? Published and accepted? John Buckleton

39. Yes you are probably right. But does this meet standards for scientific testimony? Not exactly but I’m probably right. John Buckleton

40. 20 years from now will they call this good science? John Buckleton

41. Maybe, but I suspect the difference would be much less if we had an accepted formal method for scientific decision making in forensic science. Is it not simply that reasonable people can hold different points of view? John Buckleton

42. “What if Bayesian methods can help?” John Buckleton

43. When men understand what each other mean, they see for the most part, that controversy is either superfluous or hopeless. John Buckleton