In the early 1900s, the German public was fascinated by a mathematical Mr. Ed named Clever Hans, an Orlov Trotter horse that seemed to be capable of counting, doing basic arithmetic, and even solving elementary word problems—which, lacking the dexterity to grasp a number two pencil, it would answer by stamping its hooves. Eventually, of course, it was proven that Hans was doing nothing of the sort: the horse was perceptive rather than clever, and had been picking up on subtle, subconscious cues from his handler that let him know when to begin stamping and when (having arrived at the correct answer) he should stop.
A century later, academic researchers have shown that even well-trained drug-sniffing dogs are subject to the “Clever Hans Effect,” often alerting to non-existent drugs or explosives in locations where their human handlers have been falsely told they were present. Nor are those findings strictly academic. A recent analysis by reporters at the Chicago Tribune found that field records showed that drug-sniffing dogs produced a disturbingly high level of false positives: in only 44 percent of cases where dogs alerted did a subsequent search turn up contraband. Their success rate was even lower when it came to certain minorities: when dogs alerted on a Hispanic driver, only 27 percent of ensuing searches found any drugs, suggesting that the pooches may be picking up on their handlers’ subconscious bias, effectively legitimizing a form of racial profiling.
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