October 06, 2008

Pro moron

Error, room not foundThis made my day: Ben Goldacre linked to my post on the Durham study in his miniblog, writing "A pro weighs in on the morons." Of course, it could mean that I'm a professional moron (something I want to be open-minded about... sometimes I wonder).

Apropos idiots, I have admired the many kinds of idiot-proofing computer components this weekend while building my new system. To me every connector that absolutely refuses to insert the wrong way is an engineering marvel we should admire: imagine how much grief they have saved! From the asymmetries of processor capsules and bus connectors to the SATA ports. The only break in this idiot-proofing I saw was the identical USB and Firewire connectors on the motherboard, where the case leads actually could be mis-connected with potentially bad results. Poka-yoke is something I try apply more and more in my life - given existing research I know just how unreliable my (and other's) memory and cognition is, so it would be irrational not to add simple behaviour-shapers to improve the correctness of my behaviour. So these days I put my charging cellphone in my shoe, so I will bring it with me when I leave.

Apropos the human error website, it refers to a study that probably demonstrates the lower bound on how error-free any voluntary human activity can be. Rabbit [1990] tried flashing one of two letters on a display screen. The subject hit one of two keys in response. Even after after correction the error rate per choice was 0.6%. There are a few slightly lower error rates for other simple tasks, but personally I think 0.5% is a good rule-of thumb as the lowest possible human error rate. Any task requiring fewer errors must incorporate error-detection (which, when done by humans, seem to catch 80% or errors per pass) and error-correction.

If you really need to avoid errors, use several independent passes and checks, ideally with poka-yoke. But it seems that a smarter approach is to recognize that errors will occur anyway (since the defensive design is done by error-prone and finite humans) and ensure that when they happen they fail securely.

Posted by Anders3 at October 6, 2008 04:58 PM