Evaluation of empirical methods and methodological foundations of human left-handedness

The methodological and empirical foundations underlying the theories on human left-handedness are examined, including the definition and classification of left-handedness, its relation to pathology, and the results on family, adoption, and twin research. It is argued that major research findings on left-handedness are based on inadequate empirical methods, and the concrete definitions and assessment procedures do not meet validity and reliability criteria. This also casts doubt on the relationship between left-handedness and pathology reported in the literature. Furthermore, findings from family, adoption, and twin studies do not allow interpretation of possible direct genetic contributions to explaining left-handedness. It is concluded that the methodological limitations of a causal explanation should encourage an examination of the epistemological and methodological premises of theory formulation. The functional method and a theoretical framework based on early childhood experiences and the neural plasticity of the brain may be more appropriate for the selection of empirical methods in research of human left-handedness.