A 13- member commission headed by the Philosophy Professor Carl Stumpf came to the conclusion that the clever Hans were no tricks in the game in 1904. After this clear statement competent experts examined Oskar Pfungst, a graduate student cone, the matter more closely and found a solution to the puzzle. He systematically varied the possibilities of the horse, to see someone who knew the answers to the questions. The significant result of his study was: Only if Hans could see people who knew the answer (eg, its owner, Wilhelm von Osten or the audience ), he could also be expected. Published in 1907 Pfungst his study and helped so that experimental psychology to break through.
The investigation errors discovered by Pfungst was initially referred to as the " Clever Hans effect"; Today he is known in psychology and social science rather than " interviewer effect".
- The Clever Hans. A contribution to the non-verbal communication. 3rd ed Frankfurt: Frankfurt Fachbuchhandlung of Psychology, nd ( Reprint of the original from 1907). ( First English translation 1911)