Presentation on theme: "ESR John Buckleton ood Forensi S ien e. ESR John Buckleton Good Forensic Science A view from the bottom by John Buckleton With thanks to my great mentors."— Presentation transcript:
ESR John Buckleton ood Forensi S ien e
ESR John Buckleton Good Forensic Science A view from the bottom by John Buckleton With thanks to my great mentors Ian Evett and Bruce Weir
ESR John Buckleton What can the 80s and 90s teach us? n In most cases the interpretation arguments were never settled. n They were superseded by technology or they remain n Product rule or not? n The place of independence testing? n Relatives? n Two stain at a scene
ESR John Buckleton Why we have been unable, by science alone, to settle the interpretation matters of our day?
ESR John Buckleton WHAT IS THE QUESTION?
ESR John Buckleton Budowle B. National Forensic Science Training Centre, Florida, The germane question is: What is the frequency in the database?
ESR John Buckleton n First germane. Oxford gives this as: Relevant, pertinent to the matter or subject. n It must certainly be agreed that it is important to ask relevant questions so it certainly seems important to define the germane question.
ESR John Buckleton n Since this question is germane let us try answering it. n 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? n We can now answer the germane question:
ESR John Buckleton What is the frequency in the database? The frequency in the database is zero Hmmmm. What shall I do with that information?
ESR John Buckleton Budowle B. National Forensic Science Training Centre, Florida, The germane question is: What is the frequency in the database? The frequency of what?
ESR John Buckleton The frequency of what? n The suspects profile? n The crime stain profile? n Persons who could produce the crime stain profile? n The major profile in a mixture? n Persons not excluded from this mixture?
ESR John Buckleton n The question, if taken literally, is not much use. n If it cannot be taken literally then can the question be improved? n Perhaps the author didnt mean database n perhaps he meant population.
ESR John Buckleton What I meant was, the germane question is: What is the frequency in the population?
ESR John Buckleton n Here the last word has been changed from database (where the frequency is zero) to population? n This seems quite a lot better. n Armed with this, we approach our database of 200 persons and attempt to answer this germane question. n What can we do next?
ESR John Buckleton n What has happened is that we have changed from database n completely characterized n we can count any frequencies n to talking about a population n There is uncertainty about the population. n do not KNOW the frequency of the genotype in the population. n may even have difficulty defining the population.
ESR John Buckleton n Accept that we are now estimating something n There is uncertainty in the estimation process. n We will need, at least: n A population genetic model. n A statistical theory to assess sampling error. n Estimation of something very small is difficult.
ESR John Buckleton What I really meant was, What is the product rule estimate from this database? It would be sad if the audiences positive reaction was because they liked the simplicity of this statement or that they knew how to do it or that they didnt have to learn anything new.
ESR John Buckleton Evett IW. (1983) What is the probability that this blood came from that person: A meaningful question? J Forensic Sci Soc 23: What is the probability that this blood came from that person?
ESR John Buckleton n The second was set up deliberately to answer a question of relevance to the court. n The first did not start from this formalized line of thinking. n The second is the more germane question.
ESR John Buckleton n This is the lesson that can be taken from the analysis of this question: n If you dont have some firm principles on which to base your forensic thinking you can be left relying on your intuition. n Sometimes this will be adequate but it will seldom stand up in comparison to a professional, scholarly and logical approach.
ESR John Buckleton Uniqueness?
ESR John Buckleton 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?
ESR John Buckleton I mean it has met objective criteria developed by my laboratory. What are these criteria?
ESR John Buckleton We defined a reasonable degree of scientific certainty by setting an acceptable error rate for this decision. Ouch. Thats really my job
ESR John Buckleton We ignored all issues regarding relatedness. Why?
ESR John Buckleton We assumed a population genetic model called the product rule. Ouch. How can you be sure that is correct?
ESR John Buckleton We assumed a population genetic model called the product rule. Would it be better to accept that there is some uncertainty in the model?
ESR John Buckleton Ive done lots of data analysis and I think it is OK or near enough. This sounds more like an opinion than an objective criterion.
ESR John Buckleton This is a fallacy. Independence testing cannot prove the product rule Independence testing shows that Im right.
ESR John Buckleton They are also consistent with minor subdivision Yes, but the data are consistent with expectation for independence..
ESR John Buckleton n CaucasianEastern PolynesianWestern Polynesian n PrPrPr n VWA n THO n D n FGA n D n D n VWA/THO n VWA/D n VWA/FGA n VWA/D n VWA/D n THO1/D n THO1/FGA n THO1/D n THO1/D n D8/FGA n D8/D n D8/D n FGA/D n FGA/D n D21/D
ESR John Buckleton
ESR John Buckleton Post hoc rationalization n Most unwise n Budolwe et al. n testing the FBIs HBGG locus, appear to have combined the A and C alleles. n There is a significant departure from independence if the alleles are not combined, caused largely by a single CC homozygote.
ESR John Buckleton Post hoc rationalization n Result does not appear in the paper n Budowle et al. conclude that the data are consistent with Hardy-Weinberg expectations n This is an unreasonable statement considering the (presumably) post hoc combination of two alleles.
ESR John Buckleton We BELIEVE n That the effects of subdivision are relatively minor n They do, however, add across loci
ESR John Buckleton OK so its minor so we can safely ignore it. It has no forensic significance. I wont dare ask what Forensic significance means. Would it not be more scientific to quantify the effect?
ESR John Buckleton 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.
ESR John Buckleton 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?
ESR John Buckleton 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
ESR John Buckleton Has the SCIENTIFIC basis for statements of common source in DNA been really thought through? Published and accepted?
ESR John Buckleton Yes you are probably right. But does this meet standards for scientific testimony? Not exactly but Im probably right.
ESR John Buckleton 20 years from now will they call this good science?
ESR John Buckleton 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?
ESR John Buckleton What if Bayesian methods can help?
ESR John Buckleton When men understand what each other mean, they see for the most part, that controversy is either superfluous or hopeless.