The science of handedness has baffled us from time immemorial. We explain it by dominance of one side hemisphere over others.

The study

There is a beautiful and large study about handedness. In the biggest ever global study of handedness researchers from across Europe, led by the National and Kapodistrian University of Athens and in the UK by the University of St Andrews, have concluded that 10.6% of the world’s population are left handed.Details of the study of more than two million people by researchers at the National and Kapodistrian University of Athens, University of Oxford, University of Bristol, Ruhr University Bochum and St Andrews are published in Psychological Bulletin today.

Original Research: Closed access

“Human handedness: A meta-analysis”. 

Papadatou-Pastou, Marietta,Ntolka, Eleni,Schmitz, Judith,Martin, Maryanne,Munafò, Marcus R.,Ocklenburg, Sebastian,Paracchini, Silvia.
Psychological Bulletin 

doi:10.1037/bul0000229.

Impact Statement

Public Significance Statement: To date, this meta-analysis is the largest reported study to estimate the prevalence of left hand preference for different manual tasks across geographical areas (n = 2,396,170 individuals). It shows that the best estimate for the prevalence of left-handedness is 10.6%. However, this value varies between 9.3% and 18.1%, depending on how handedness is measured. The same evolutionary mechanisms should apply to participants of different geographical ancestries to maintain the roughly 1:10 ratio of left- versus right-handers found worldwide. The exact prevalence of left hand preference is moderated by cultural factors, primarily pressure to change writing hand, possibly because of direct instructions by parents and teachers and also through nonexplicit model learning. More data is needed for individuals with less represented ancestries. When 3 handedness categories are given (left-handed, mixed-handed, and right-handed), the best estimate for the prevalence of mixed-handedness is 9.33%, a number almost as large as the prevalence of left-handedness. This highlights the importance of taking this group into account in future handedness studies. Hand preference measurement moderates the estimated prevalences of left- and right-handedness. We urge researchers to define universal criteria for measuring hand preference (short questionnaires, reporting both writing hand and Edinburgh Handedness Inventory [EHI] scores, and reporting at least 2 classifications, e.g., R-L and R-M-L), as measurement imprecision and/or heterogeneity affects the estimated prevalence. Moreover, studies need to fully report study characteristics, such as instrument used to measure handedness (including questionnaire length and individual item content), response format, classification scheme, country in which the study took place, as well as population characteristics, such as sex, age, ancestry, and educational and sporting level of the participants, ideally by uploading raw data in open-access repositories. Detailed reporting is essential to compare effectively between different studies as well as to encourage good study design. (PsycInfo Database Record (c) 2020 APA, all rights reserved)