Math and The Law

  When I was researching more on the math used by forensic scientists, I came across a couple things on math and the law which I found so interesting, I thought I'd share them with you.

Let's start with the Amanda Knox case.  In case you don't remember, she and another person were prosecuted in Italy for the murder of another person.

After being convicted, they appealed the court decision.  They won that but then the acquittal was thrown out over mathematics.

Their conviction was based on the identified DNA on the "murder" weapon.  The sample was quite small and back in 2009 the testing at that point could not provide a reliable result.  In 2011, when the appeal hit the courts, the judge decided that retesting the material would not provide any better results because the sample was smaller.  He ignored the part stating, testing methods had improved to the point of increased reliability of the results.

The court overturned the overturn because they felt the judge did not understand that if a test is run twice and it yields the same results, we can assume the first test was reliable. 

In another case, a Dutch nurse was convicted of murdering people on her watch.  The prosecution witness used incorrect methodology to state there was a 1 in 342 million chance of the deaths being natural.  So the jury convicted her.  After a long fight, that included a panel of statisticians, it came out the odds were wrong and the deaths were natural.

Another case of wrongful conviction based on bad math, involved a young English mother convicted of murdering her two children, both of whom died of crib death.  The conviction was based on a prosecution witness who claimed the chances of this happening in one family was one in 73 million.

Again, after a long fight and the involvement of the Royal Statistical Society, it was shown the basic method used to provide the probability had been flawed.  The women's conviction was overturned but the experience changed her.

Another case involved a couple who were convicted of a robbery based on the incorrect assumptions  applied to the multiplication  rule of probability as explained by a mathematician. The basic probabilities were calculated as independent events rather than conditional.  In other words, they treated The female who was blond and wearing a pony tail as 1. a white female with a pony tail and 2. A white female with blond hair rather than a white female who wore her hair in a pony tail. They were able to show the flaws in the math, and the conviction was overturned.

These are some ways math has been used incorrectly in trials.  Its a nice way to show how math can be incorrectly used to convict people.  Let me know what you think, I'd love to hear.