Clever Hans and Usability Tests

Lukas Mathis retells a nice story that illustrates a hidden bias that can pollute a usability test.

Clever Hans, his horse, quickly learned to do a number of complex math calculations – the horse could add, subtract, multiply, divide, do date calculations, and even understand German. It would tap out the answers to any math question with its foot. It could even read and give the correct answers to questions written on a piece of paper.

Of course, when psychologist Oskar Pfungst investigated the horse, he quickly figured out what was happening. The horse didn’t understand German, couldn’t calculate, and couldn’t read. Instead, it responded to involuntary cues in the body language of Wilhelm von Osten, who, in turn, solved the math problems for his horse. Von Osten was completely unaware that he was providing these cues to the horse.

Sep 1 2009

I believe there was an episode of Frasier based on this.