Independent dimensions of hand preference: reliability of the factor structure and the handedness inventory

Healey, Liederman, and Geschwind (1986) suggested that handedness is not a unidimensional trait. They devised a questionnaire with 55 handedness items and 6 familial hand preference items and administered it to 290 adults. Their analysis identified four independent factors underlying hand preference. In the current study, the reliability of all but one of the items on the original inventory was established by retesting 83 of the original subjects. An additional analysis revealed that approximately 2% of the population could be considered to have "ambiguous" handedness in the sense that they indicated unstable hand preference according to the criteria suggested by Soper and Satz (1984). The reliability of the factor structure was evaluated by factor analyzing data from a new sample of 487 subjects, demographically similar to those in the original sample. All four factors reappeared with minor shifts in item loadings. The original and second samples were then combined, and four factors were again found, even when the sample was reconstructed so that there were equal numbers of males and females. On the basis of these new analyses our initial conclusion was confirmed: hand preference must be characterized along more than one dimension.