An email from Forensic Bioformatics alerted me to yet another rather surprising problem with the dreaded magic of DNA. I, like most lawyers, maintain a somewhat idealized vision of science. While “junk science” has long been on my radar, “real science” is still on a pedestal, mostly because I want to believe that somebody out there is more dedicated to the truth than to the conviction. Naive, as we well know, but still true.
Bioforensics, however, burst my bubble again by alerting me to yet another problem with DNA testing, the Context Effect. As we push to improve identification procedures in light of the overwhelming studies that show that eyewitness IDs are replete with flaws, it appears that many of the same problems exist with DNA.
Picture the DNA analyst given a sample from a suspect in a crime and asked to compare it for a match to a sample found at a crime scene. That’s the scenario address in this White Paper by Bioforensics. The analyst, knowing what he’s dealing with, will try very hard to make the match, and his knowledge of what he’s got in hand will influence the way he “interprets” fuzzy areas. Objective interpretation becomes subjective, and fuzzy becomes clear when the analysts knowledge affects his judgment.
When I asked if there were any good examples of this happening, a big one came back at me.
Examples of context effects in forensic science are unfortunately not difficult to find. One of the most famous is the Brandon Mayfield case, where several FBI fingerprint experts “matched” his print to fingerprints found on a bag of explosives material found in connection with the Madrid train bombing. The FBI’s fingerprint software listed Mayfield as a potential match, so the analysts were more likely to try to match the prints. Mayfield was later found to be completely innocent.
That’s certainly a fairly clear example of how objective science turns subjective. Jason Gilder has provided me with a powerpoint showing the problem in more scientific terms,
I just wanted to thank you for blogging about this issue. I have seen it in my practice and it needs to be exposed for exactly what it is. Kudos to you!
Maybe I’m missing something (I am not an attorney), but isn’t this the same issue as the effect of observer bias and placebo effect in scientific investigations? It has long been recognized that these effects exist and can be large; hence the necessity to employ double-blind procedures, especially in clinical studies where subjective judgements can enter into the data. Well established protocols and methods are available and could be easily applied in DNA analyses as well as identification lineups, etc.
You are absolutely right. But I (as a lawyer) was unaware that this problem existed in DNA testing as well. I assumed, wrongly, that it was not so subjective, interpretive and subject fo observer bias. While we’re still fighting for double blind identification procedures, we now have another battle to fight over DNA.
Could this be easily applied? Absolutely. There are indeed established protocols, and the White Paper proposes the protocol for DNA testing. Will it? As I said, we’re still fighting over double-blind identification procedures. The problem is clear. The solution is clear. The police and prosecutors resist it, because it makes their job harder.