Bag's Rants

DNA Matching. Not as reliable as we are led to believe.

Following on from my DNA DB article I went exploring and found some interesting things about DNA.

As an aside, the latest news was regarding the percentages of black people on the database. Read more here. But, is it surprising? The way the data is collected means that while blacks commit more crimes and are arrested there are going to be more on the database. Plus, because there is proportionally less of them in the UK, the percentage will be higher so it didn't come as big a surprise as the news seems to make it. Although, nearly half, 39% was more than I was expecting.

Back to the topic. I don't know about you but I originally believed that DNA was unique and that your DNA was never going to be found in another person.

Then I discovered it was unique in 1 in a hundred billion. That is 1:100,000,000,000. Err. How did they work that figure out? Usually through reverse engineering. They take 10,000 samples and get one duplicate or something and extrapolate it that way. If so how can they talk unique? This could mean that there is more than one of you with the same DNA. I know the current population is about six billion but statistically that could mean that there is someone with your DNA. It's only 0.06 but then the chance of winning the lottery is less than that and people win most weeks. OK then, DNA should only be used as an add on to existing evidence. It's still a reasonably good pointer but with no confession you must have some other evidence to support the crime. Unfortunately, that is not the case but it is assumed that statistically they are unlikely to pull off the street a match so they say let's not talk about false matches and still talk unique in court. What about Justice?

To make things worse it now starts to become clear that DNA and the DNA profiles we store on our databases are not the same and the chances of duplicates in the simpler DNA profiles is down to 1 in two hundred and forty thousand that is 1:240,000. A significant difference. Read more about profiling here. This guy has an axe to grind but his data seems to hold up.

That means in the UK with 60Million population there are approx 250 people with your DNA profile. In the world with 6Billion that makes it 25000. How is that conclusive proof with no other evidence?

Why do we still talk unique in court when it clearly isn't? Why is the Government so intent to build up it's DNA DB? I suppose if everyone is on it then when a crime is committed they can arrest all the matching profiles, about 250, release the ones with a clear alibi and then interrogate them, with or without waterboarding and narrow it down. Should save a lot of that pesky investigatory work and evidence finding. That seems to be the only reason I can come up with. How about justice then? His DNA matches. Guilty! And a nice quick court case.

posted by Bag @ 12:53 pm