the dynamic evidence page
Friday, March 27, 2009
Postscript to the Story of the DNA Pixie Dust in the Phantom of Heilbronn Case
the dynamic evidence page
Thursday, March 26, 2009
DNA as Pixie Dust
DNA.
More precisely, unsanitary packing procedures during the manufacturing process, perhaps.
The Spiegel story (in very rough translation) tells us:
It now appears that the chances of finding the trail of the mysterious suspect are slimmer than ever before -- because she apparently doesn't exist. According state's attorney Heilbronn, the Baden-Wuerttenberg Office of Criminal Affairs is now investigating whether the cotton swabs ["Q-tips"] that investigators used to collect DNA samples [at crime scenes] had already been contaminated with DNA and had thus led investigators on a false trail.
According to a report in Stern.de, the matter involves a packager [a packer, an employee] who worked for the manufacturer of the swabs that were used [at the crime scenes]. According to this report, the swabs were, to be sure, sterilized. But, according to Christian Rueff of the University of Zurich, such sterilization of the swabs does not affect contamination of the swabs with DNA by cells of the human body. [PT: The employee, I presume, held the cotton swabs in her hands when putting them into boxes or other containers.] The manufacturer delivered cotton swabs to various places in Germany and and also in France and Austria.
the dynamic evidence page
Wednesday, March 25, 2009
Folk physics, common sense, inference, and intelligence
Perhaps metaphysics = sophisticated folk physics.
Folk physics should make use of the insights of physics -- and much else (e.g., neuroscience).
But folk physics -- metaphysics -- should not allow itself to be displaced by, e.g., physics or neuroscience.
Do not think that matters such as common sense and folk physics are unintelligent. They harbor much intelligence. If a special science can explain them, it will prove that it too is very intelligent. (But no special science can yet explain common sense, or "ordinary" intelligence.)
Of course, physics, neuroscience, etc., have much intelligence that ordinary intelligence lacks. But this fact does not render folk physics, common sense, etc., unintelligent.
coming soon: the law of evidence on Spindle Law
Hájek: Whether You Like It or Know It or Not, You Have a Reference Class Problem
Now, the bad news. Giving primacy to conditional probabilities does not so much rid us the epistemological reference class problem as give us another way of stating it. Which of the many conditional probabilities should guide us, should underpin our inductive reasonings and decisions? Our friend John Smith is still pondering his prospects of living at least eleven more years as he contemplates buying life insurance. It will not help him much to tell him of the many conditional probabilities that apply to him, each relativized to a different reference class: “conditional on your being an Englishman, your probability of living to 60 is x; conditional on your being consumptive, it is y; …”. (By analogy, when John Smith is pondering how far away is London, it will not help him much to tell him of the many distances that there are, each relative to a different reference frame.) If probability is to serve as a guide to life, it should in principle be possible to designate one of these conditional probabilities as the right one. To be sure, we could single out one conditional probability among them, and insist that that is the one that should guide him. But that is tantamount to singling out one reference class of the many to which he belongs, and claiming that we have solved the original reference class problem. Life, unfortunately, is not that easy—and neither is our guide to life.Still, it’s better to have one problem than two. I will leave it to others to judge the extent to which I have succeeded in ridding us of the metaphysical reference class problem. But I am aware that I have not solved the epistemological problem. I invite you to join me in the search for a solution for the interpretations of probability that have a genuine claim to being guides to life. After all, whichever interpretation you favor, the epistemological version of the reference class problem is your problem too.
P.S. I suspect that a successful "solution" to the epistemological version of the reference class problem(s) requires a bit of metaphysics (i.e., some basic assumptions about [wo]man and the world [s]he inhabits).One man's metaphysics is another man's physics? Folk physics?Folk physics has its uses -- and in an important sense it may be even "true."
N.B. By putting solution in quotation marks I do not mean to assert that a satisfactory solution of some kind is impossible. (Of course, there are solutions and there are solutions: one solution will not necessarily solve -- thank goodness! -- every possible problem about the choice and use of reference classes.)
coming soon: the law of evidence on Spindle Law
Tuesday, March 24, 2009
A Practical Solution to the Reference Class Problem?
The "reference class problem" is a serious challenge to the use of statistical evidence that arguably arises every day in wide variety of cases, including toxic torts, property valuation, and even drug smuggling. At its core, it observes that statistical inferences depend critically on how people, events, or things are classified. As there is (purportedly) no principle for privileging certain categories over others, statistics become manipulable, undermining the very objectivity and certainty that make statistical evidence valuable and attractive to legal actors. In this paper, I propose a practical solution to the reference class problem by drawing on model selection theory in statistics. The solution has potentially wide-ranging and significant implications for statistics in the law. Not only does it remove another barrier to the use of statistics in legal decisionmaking, but it also suggests a concrete framework by which litigants can present, evaluate, and contest statistical evidence.
coming soon: the law of evidence on Spindle Law