To the Editor.—
The letter by Drs Pittsley and Shearn (236:819, 1976) correctly emphasizes the low sensitivity of thumbnail size in predicting handedness. A more accurate test to determine handedness was recently described by Syed.1 He found that if a person pairs the second and third fingers and also the fourth and fifth fingers of both hands and then stretches these paired fingers away from each other as far as possible, the interdigital space between these two pairs will be larger in the left hand than in the right hand in a right-handed person and vice versa.The reliability of this method was investigated and compared to the thumbnail size test in 85 persons ranging in age from 7 to 57 years. Persons who had sustained trauma to their hands or were neurologically impaired were excluded, as were children under 7 years of age, because they had great difficulty
Berman W. Determining Handedness. JAMA. 1977;237(17):1824–1825. doi:10.1001/jama.1977.03270440014005
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