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Bayes’ Ruling

“There are lies, damned lies, and statistics”

-Mark Twain

Lawyers are notorious for exaggerating the truth. When money and lives are on the line, attorneys will do whatever it takes to win, even using math. Many lawyers have applied Bayes’ Rule to strengthen their cases. There is no doubt that the correct application of Bayes’ Rule could help the justice system immensely, but it rarely happens. Judges tend to through out statistical evidence often because lawyers come up with insufficient data or misuse Bayes’ Rule. Many times, lawyers will mistake the odds associated with a piece of evidence with the odds of actual guilt. This is so common its known in the legal world as the prosecutors fallacy. For instance, in the case where a woman was accused of murdering her children, lawyers claimed that it was improbable that the children died of “cot death”. However, it is even less likely that a woman would murder her own children. In order to remedy these poor practices, ¬†an international group of lawyers and statisticians are working together to brainstorm solutions and come up with rules and regulations for statistical evidence.

When used properly, Bayes’ rule can be extremely helpful. However, the intuition behind Bayes’ rule is what often confuses people. Just like false positives in medical testing, the way information is worded can sway our opinion, even if the information is the same. It it integral that statistical evidence needs to be accurate and simple enough in order to be presented in court. In fact, using flow charts is often a great way to show a courtroom the exact probability in a clear and concise fashion.


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October 2014