Left handers make up 10.6% of the world's population, but as many as 18% could be using their left hand for one or more tasks.
Many online reports suggest an average 10% of the population is left handed. But, measuring handedness is complex and needs to consider several factors, including:
Understanding the difference between left handedness, mixed-hand dominant and ambidextrous
Are mixed-handed and ambidextrous people considered left handed; think of left-handed tennis players like Rafael Nadal who writes with his right hand, or cricket players who bat left and throw right
How handedness is measured (questionnaire, physical tasks, observations, etc)
Cultural and geographical factors resulting in pressure to try to become right-hand dominant
National and Kapodistrian University of Athens Assistant Professor Dr. Marietta Papadatou-Pastou led a team of researchers through the largest published report to date on human handedness with data from almost 2.4 million individuals. This meta analysis involved collecting data from studies that have already been published. Some studies used group participants who are left handed and right handed, while others included participants who are left, mixed, or right handed. Some studies had even more complicated classifications including many analyzing non-right handers (left and mixed-left) and right handers.
To help briefly explain classifications for certain studies on handedness, we look back at the work done by renowned researcher Dr. Marian Annett (1931–2018). Dr. Annett was especially interested in the fact that many people use their right hand for some activities while using their left hand for other tasks. She included several different classifications in her 1998 publication, Handedness and Cerebral Dominance, which recognized the fact many people are somewhere between being a strong left hander and a strong right hander. The Table below includes a brief summary of some of Dr. Annett’s subgroups. You can find the original Figure here and original Table here.
What Percentage of the Population is Left Handed
Dr. Papadatou-Pastou says there isn’t a clear consensus “on how to measure handedness and how to categorize people into these different categories. When we collected all these different datasets from all those studies, we had to make it work and so we tried different groupings as well as this overall grouping of participants, and we couldn't do just one single overall analysis." The 2020 publication shows, “left-handedness prevalence lies between 9.3% to 18.1%, with the best overall estimate being 10.6% (10.4% when excluding studies assessing elite athletes’ handedness).” Dr. Papadatou-Pastou says, "When we consider the most stringent criteria for left handedness---the criteria used by studies with group participants who are left, mixed or right handed---so if you only take into account those left handers who have been distinguished from mixed handers, you get 9.33% as a prevalence of left handedness.” When Dr. Papadatou-Pastou’s team considered all left, mixed and non-right (left and mixed-left) handers as left handers from the different studies---those studies examined classifications such as left and right handers…left, mixed and right handers…and non-right vs right handers---they said this was the most lenient criterion and therefore arrived at a much higher percentage of 18.1% of left handers.
As you can see, accurately measuring left handedness is not an easy task. But, Dr. Papadatou-Pastou and her team have established an estimated percentage of global left handedness based on a large sample size and detailed analysis. “I have been a researcher in the field of handedness and laterality for more than 15 years,” says Dr. Papadatou-Pastou. “Every time I would read a paper it would say, ‘left handers are about 10% of the population’ and then they would reference some large or not so large-scale study. Up until now we didn't have one estimate that would take into account all research that is out there. So, I'm really proud we did that, and our study has the most power compared to all other studies because it integrates all previous studies that have been published on the prevalence of left handedness. And let me here say that we only included studies that gave separate percentages for males and females because we know there is a robust sex difference in left handedness. So, I'm proud because we managed to estimate a specific number and now we no longer have to say in our papers ‘left handedness is about that (estimated number).’ The other thing I'm proud of is we managed to show mixed handedness is a category that is almost as large as left handedness. More than 9% of people are mixed handed and this is something that we should look into more in the in the future.”