Left-Handedness: What Is Right-Hand Bias?

What is right-hand bias?

Sometimes, it can be hard to be a left-hander: Many things we use in everyday life have been designed for right-handed use such as scissors, or pens. Moreover, in many social situations, we are expected by others to do certain things with the right hand, such as shaking hands when greeting somebody else. In his recent book, “How Handedness Shapes Lived Experience, Intersectionality, and Inequality—Hand and World,” philosopher Peter Westmoreland from St. Petersburg College in Florida discussed these and similar phenomena under the term right-hand bias (Westmoreland, 2023, see here for a review of this book that I have written). In short, right-hand bias describes the idea that across countries and cultures, people are implicitly required to act like a right-hander in many contexts and that it is considered unusual to use the left hand for many activities. In general, there is a bias that privileges the right hand over the left (Westmoreland, 2023).

Assessing right-hand bias in psychology and neuroscientific studies

One important question is whether right-hand bias is merely a philosophical idea based on anecdotal evidence or whether there is some hard data to back it up.

Interestingly, there is some very convincing evidence that right-hand bias does indeed exist.

In 2019, scientist Lyam M. Bailey from the department of psychology and neuroscience at Dalhousie University in Halifax, Canada, and co-workers published a scientific paper in the European Journal of Neuroscience in which they analyzed data on handedness‐based recruitment biases in neuroimaging publications (Bailey and colleagues, 2020). Unfortunately, it is common practice in psychological and neuroscientific research that scientists either do not recruit left-handed people, to begin with, or they later exclude them from data analysis. This is often done because left-handed people sometimes show brain asymmetries that are different from right-handers. For example, while almost all right-handers show a dominance of the left hemisphere for language, right-hemispheric language dominance is much more common in left-handers. The scientists then exclude left-handers to ensure that their overall data patterns in the sample do not show too much variability, which could be problematic with statistical analysis. This is of course a classic example of right-hand bias, since right-handers are considered the norm, while left-handers introduce unwanted variability in the data and are this excluded.

Left-handers are clearly underrepresented in psychology and neuroscientific research

What did the scientists find?

They analyzed data from 1008 scientific articles published in prestigious scientific journals which included handedness data for 31,973 people, a sizeable number. Overall, 97 percent of the participants in these studies were right-handed, while about 3 percent were not right-handed, so either left-handed or mixed-handed. Since it is well known that 10.6 percent of people are left-handed (Papadatou-Pastou and colleagues, 2020) these findings clearly show that scientists show right-hand bias when recruiting participants for their studies and recruit left-handed people to a lower extent than they are present in the overall population.

This is of course a problem, since it may reduce what we can learn from these studies about the human brain. People show variations in brain structure and function, and to get real insights into the brain such variations should not be excluded from studies. Making people aware of right-hand bias and encouraging scientists to include left-handed participants in their studies is therefore highly important to assess the full diversity of the human brain in neuroscientific research.