How well do you know the back of your hand? Toward evidence-based knowledge

Familiarity with the back of one's hand has long been used as a reference criterion for knowledge despite a lack of supporting evidence. The present study prospectively tests normal subjects' knowledge of dorsal hand features. Sixty surgical, medical, and allied hospital employees (30 men, 30 women) were asked 5 questions with binary answers about features on the dorsum of their dominant hands while their hands were concealed. The proportion of correct answers to each question ranged from 0.45 to 0.65, and none was significantly different from 0.50. Similarly, the mean percentage of correct answers for all subjects and all questions was 54%, which was not significantly different from 50%. Thus, the accuracy of the answers approximated random guesses. Hand specialists scored significantly higher (75%) than other occupation groups. Men and women scored equally as a whole. These data refute the use of the hand idiom as a reference criterion for knowledge.