19 February 2011

Not so Clever Hans

I've blogged about this before but it seems as though others are catching up.

In short, the police powers of stop and search are found in the section 1 of the Police and Crimanal Evidence Act 1984, where s1(3) PACE 1984 provides,
"This section does not give a constable power to search a person or vehicle or anything in or on a vehicle unless he has reasonable grounds for suspecting that he will find stolen or prohibited articles"
When police use sniffer dogs as a basis for stopping and searching people is this lawful?

It depends upon whether or not the sniffer dog behaviour gives the officer reasonable grounds.

We can only answer that question if we know the (i) false positive rate, (ii) false negative rate, and how the Clever Hans effect is prevented.

The Clever Hans effect being a mechanism whereby the animal's behaviour is a result of unwitting cues given to it by its trainer.

Well, it seems that someone has decided to bother investigating the Clever Hans effect with regard to sniffer dogs - here's a link to the Mind Hack's article that has more details, Sniffing Out the Unconscious.

Link to original article dx.doi.org/10.1007/s10071-010-0373-2.

My previous notes,


  1. I guess it also depends on what kind of day the sniffer dog is having, and whether the suspect was silly enough to carry a tasty treat around in his pocket along with the half pound of heroin.

    What if the dawg smelt out, say, a gingters pasty* secreted somewhere on the suspect and he alerted the officer to the suspect on that basis? Could that technically have been an unlawful stop and search? ;-)

    I guess you'd hope those kind of inclinations would be groomed out of the dogs during training, but you never know.

    *The dog clearly didn't have very discerning tastes if he's partial to a gingsters pasty but I was struggling for an example! :-)

  2. You're doing an Us and Them thing in your first paragraph, Michael: you're assuming the suspect is guilty and hence worthy of a crappy screening assay.

    Re-writing gives,
    "...and whether the suspect was silly enough to carry a tasty treat around in his pocket along with the [pork pie / dictionary / mobile 'phone / any innocuous item that an innocent person may be carrying, which does not amount to reasonable grounds]."