How should "ambidexterity" be estimated?

Weak and absent hand preferences have often been associated with developmental disorders or with cognitive functioning in the typical population. The results of different studies in this area, however, are not always coherent. One likely reason for discrepancies in findings is the diversity of cut-offs used to define ambidexterity and mixed right- and mixed left-handedness. Establishing and applying a common criterion would constitute an important step on the way to producing systematically comparable results. We thus decided to try to identify criteria for classifying individuals ambidextrous, mixed right- or left-handed or strong right- or left-handed. For that purpose, we first administered a handedness questionnaire to 716 individuals and performed multiple correspondence analyses to define handedness groups. Twenty-four participants were categorized as ambidextrous (3.3%), as opposed to mixed (29.2%) and strong (56%) right-handers, and to mixed (9.1%) and strong (2.4%) left-handers. We then compared this categorization with laterality index (LI)-based categories using different cut-offs and found that it was most correlated with LI cut-offs at -90, -30, +30 and +90, successively delimiting strong left-handedness, mixed left-handedness, ambidexterity (-30 to +30), mixed right-handedness and strong right-handedness. The characteristics of ambidextrous and lateralized individuals are also compared.