31-05-2013, 11:10 AM
Phil Thomas Wrote:Just suppose that my DNA was on file.
A legal expert states in court that the chances of both me and a murder having the same DNA is one in a million.
Am I guilty beyond reasonable doubt??
If one in a million means that that for both parties there is a 1 in 1,000 chance of having that DNA type then.
There would be 6,000 suspects spread across Scotland and another 50,000 plus in England.
Except that the chances of DNA evidence being incorrect are widely regarded as being somewhere in the range of 1 in 3 billion to 1 in 20 billion. That's at least 3000 times more unlikely than your 1 in a million, and means that by even the most conservative estimate there is statistically only one other person on the planet with a close DNA match to you (identical twins excluded). But that would be with a standard DNA test which looks at hundreds of base pairs. If you were to look at the whole genotype of a person (which can be done these days), then you'd find an exact match is pretty much impossible.
Phil Thomas Wrote:I plead (still hypothetically) not guilty. The court should demand extra evidence before convicting on this type of evidence.
A court wouldn't necessarily convict you using this type of evidence. It would use the evidence to say for certain that you were at the scene of the crime. Essentially, a court considers DNA evidence to be conclusive proof that a person was at the scene of a crime. It's as much a fact as seeing them there on CCTV footage.
Phil Thomas Wrote:For move analysis. Perhaps Ivanov owns and plays against Houdini. It would be valid for Ivanov to know when siting down for a tournament game that Houdini rates I e4 above 1 d4 and that against the Sicilian best moves are 2 Nf3 and 3 d4 and 4 Nxd4. That would be 10% of a game with perfect matches. If he is a 2000 plus player he will probably memorise longer lines than that.
Analysis of Ivanov's games started in the middle game to avoid opening theory from skewing the results.
Phil Thomas Wrote:No winner of the UK lottery winner ever gets investigated even though the odds of selecting the correct 6 numbers is 1 in 14,000,000. I have heard many stories over the years of winners who used their relative's birthdays to choose their lottery numbers. That explanation would simply not stand up in court.
But lots of people play the lottery, making it very likely that someone will win it. To make it possible that someone was not at a crime scene but someone else with a very close match to their DNA was, everyone on the planet other than the accused would have needed to - statistically - have been at the crime scene. And even then, there is a very reasonable chance that a DNA match to the accused would not be found. The two aren't comparable.
