Forensic Pseudoscience (2015)
bostonreview.net
bostonreview.net
This expert, paid by the litigant, had written a few papers for low-quality journals and taught at a class at a west-coast medical school on forensics. His written claims supporting the lawsuit were provided to the defense and he was questioned in a deposition.
The expert's conclusions in his report were based on bad probability. This was several years ago so I don't remember all of the details, but one error was the using 50% as a prior probability because the actual prior condition wasn't known and could have been one of two possibilities, X or not X; 50% was picked because there were two possibilities and disregarded the relative rarity of X in the general population. Another error was really quite laughable, at one point essentially arguing that P(A & B) = P(A) + P(B). All of this was hidden by somewhat confusing language.
It really wasn't a laughing matter because the lawyers, which had asked me to explain the report to them, couldn't understand the probability well and were consequently unsuccessful in exposing the expert's faulty reasoning during his deposition. Fortunately, the expert's so called report was not introduced at trial and he wasn't called upon during the trial.
I don't remember the exact numbers used in OJ Simpson's trial but the rationalization used is more important than the numbers. His lawyer argued that some very small percentage of men who beat their wives later go on to murder them. Therefore, the fact that OJ beat his wife shouldn't factor into his trial at all. The fundamental flaw in the argument is that there was no question on whether or not his wife was dead. We knew she was dead, so the correct statistic to look at would be, of women who were beaten by their husbands and later murdered, how often was the husband the murderer? And the answer was some large percentage, like more than 90%.
Sally Clark's case was even sadder. She was eventually released from prison but committed suicide not long after. She was on trial for murder after her second child died from SIDS, her first child having died the same way. The prosecution brought in an "expert witness" to give the probability of one woman having two children die from SIDS. All he did was take the incidence of SIDS at the time, 1 in 8500, and square it, coming up with 1 in 75 million. No other evidence of murder was found, she was convicted because of the statistical argument. This argument has multiple flaws. It assumes that the two incidences of SIDS in this case were independent events, which is not necessarily the case. On top of that, even if you could assume they were independent events, a 1 in 75 million event doesn't mean the event is impossible. A person should not be convicted on that probability alone with no other evidence.
there are certainly a number of forensic fields which are garbage.
other portions are fine, and are effectively analytical chemistry applied to legal cases. are you aware of a lot of double blind studies in analytical chemistry? what would that even mean?
I gave an example at the top level comment. Apply the test (blind) to known innocent samples too, and see whether it implicates them.
many of the state lab testing scandals would be discovered years earlier if defense lawyers regularly had things retested.
Convicting a poor black man who dropped a cigarette butt at the scene hours prior to the crime may ultimately be far easier than finding the actual perp.
If prosecutors were punished for every conviction that is later overturned then they might be more reluctant to push for conviction on flimsy fabricated evidence.
The logical thing to validate is the actual underlying science that is vastly easier to tease out and test independently and scientifically if we haven't even tried to disprove something it has limited merit and historically if its proponents resist even trying to prove it it is almost certainly hokum.
Wherein the means to test and validate the means we are using to deprive people of their freedom and sometimes their lives represents a fraction of the budget of the criminal justice system we are guilty of malpractice as a society.
This isn't something you can casually shrug off.
This assertion is entirely inline with proper scientific thinking.