When metrics mislead: The conceptual costs.

This commentary evaluates the conceptual and methodological challenges in handedness research, focusing on the implications of prevailing measurement practices. Although handedness has traditionally been viewed as a binary trait (left vs. right), the widespread adoption of psychometric instruments has introduced a degree of continuity that may not accurately reflect its underlying biological structure. Scales, such as the Edinburgh Handedness Inventory, generate continuous scores that are frequently partitioned into arbitrary categories, leading to conceptual ambiguity and limited comparability across studies. The assumptions that hand preferences are inherently continuous and that handedness is a multidimensional trait with equally significant dimensions are challenged. Instead, it is argued that dimensions, such as the "degree" or "consistency" of hand use, may reflect contextual and probabilistic variation rather than independent latent factors. Drawing on analogies from biology and psychiatry, a hybrid structure is proposed, in which discrete latent categories coexist with graded phenotypic expression. To address this complexity, two less well-known methodological approaches are described: taxometric analysis, which identifies categorical latent structures, and fuzzy classification, which captures graded membership without the imposition of artificial or "crisp" boundaries.