Evidence in support of UK DNA database is "most unclear and badly presented piece of research"

The British Home Office want to keep a huge DNA database of people who've been acquitted of crimes (or arrested and then released with charges dropped), saying that "innocent people who have been arrested are as likely to commit crimes in the future as guilty people." In support of this "controversial assertion" they cite a piece of research that Guardian science columnist Ben Goldacre calls "possibly the most unclear and badly presented piece of research I have ever seen."

On page 30 they explain their methods, haphazardly, scattered about in the text. They describe some people "sampled on 1st June 2004, 1st June 2005 and 1st June 2006". These dates are never mentioned again. I have no idea what their plan was there. They then leap to talking about Table 2. This contains data on people each from a "sample" in 1996, 1995, and 1994, followed up for 30 months, 42 months, and 54 months respectively. Are these anything to do with the people from 2004, 2005, and 2006? I have no idea.

In fact I have no idea what "sample" means, perhaps that was the date they were first arrested. I don't know why they were only followed up for 30, 42, and 54 months, instead of all the way to 2009. Crucially I also don't know what the numbers in the table mean, because they don't explain this properly. I think it is the number of people, from the original group, who have subsequently been arrested again.

Anyway. Then they start to discuss the results from this table. They say that these figures show that arrested non-convicted people are the same as convicted people. There are no statistics conducted on these figures, so there is absolutely no indication of how wide the error margins are, and whether these are chance findings. To give you a hint about the impact of noise on their data, more people are subsequently re-arrested over the 42 month period than over the 54 month period, which seems surprising, given that the people in the 54 month group had a much longer period of time over which to get arrested.

Is this a joke?

[stumo July 20, 2009 1:17 AM]

I am very glad that Ben Goldacre writes columns in a national newspaper. I wish he could get his message across more widely.

[Takuan July 20, 2009 1:29 AM]

I don't think they really need accurate samples or rigorous methodology. The whole idea of a "database" is that a "database" be said to exist. Then when they want to hang someone they can say they have "DNA evidence", since of course everyone "knows" a "database" exists.

Think I exaggerate? Take a look at the history of DNA evidence and false convictions in the USA. Sloppy lab work, lost records, out and out lying by technicians all to produce the desired conviction. The work it backwards to "prove" the guilt of the already decided guilty.

[ackpht July 20, 2009 1:37 AM]

"innocent people who have been arrested are as likely to commit crimes in the future as guilty people."

If innocent people who have not been arrested are less likely to commit crimes in the future than innocent people who have been arrested, then don't arrest innocent people, because doing so only increases the crime rate.

If innocent people who have not been arrested are as or more likely to commit crimes in the future than innocent people who have been arrested, then arrest everyone- because everyone will eventually commit a crime.

[Takuan July 20, 2009 1:45 AM]

heh! one of the traditional justifications for terrorists to murder the innocent is that "everyone is guilty!"

[Klink July 20, 2009 3:27 AM]

Ah bravo! Another database, that'll show 'em young hooligans what for!

[Telecustard July 20, 2009 5:39 AM]

"innocent people who have been arrested are as likely to commit crimes in the future as guilty people"

Boy, that just says it all, doesn't it? We're all criminals, and they're eventually going to get all of us for something, it's just a matter of when, so they may as well keep whatever gets caught in the big, big net. It means that they want the database to eventually include everyone, no doubt. "Innocent" is as outdated a term as "privacy".

Captcha: yarmulke had

[The Unusual Suspect July 20, 2009 10:01 AM]

On the other hand, the attitude of many police forces being what it is, I do believe that innocent people who have been arrested are as likely to be arrested again in the future as guilty people.

[Bugs July 20, 2009 10:50 AM]

"Innocent people who have been arrested are as likely to commit crimes in the future as guilty people."

I think the way this is phrased is very telling of the police's attitude. They could just as easily have said

"In general, people found guilty are no more likely to commit crimes in the future than innocent people."
If that's true, it makes no sense to store DNA samples for anybody.

I know it's not a perfect argument; police tend to arrest people from groups that are statistically more likely to commit crime (e.g. poor young men), so it's not reasonable to compare the group "people who've been arrested" with the entire population. But individuals in those groups have exactly the same right to be presumed innocent as e.g. my grandmother does. Simply being poor and male (or in any other groups the police tend to target) shouldn't mean you don't get that right.

Once again, it's the presumption of guilt; we're all considered guilty unless we repeatedly prove to the state that we're innocent. That's not how a free society is supposed to work.

[Takuan July 20, 2009 5:14 PM]

http://www.youtube.com/watch?v=BnejNGprm3I