Left handed IQ is essentially the same as right-handed IQ: a meta-analysis of 20,442 people found an average gap of about one point, a negligible difference.
Dr. Russell T. WarneChief Scientist
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Left-handed people are not smarter or less intelligent than right-handed people in any way that matters. The largest meta-analysis of left handed IQ found that right-handers scored about one IQ point higher on average, a difference the authors called negligible, and even that small gap disappeared when the single largest study was removed.
Handedness has attracted claims in both directions for more than a century, from the idea that left-handers are creative geniuses to the idea that they are at a disadvantage. This page covers how common left-handedness is and where it comes from, what the IQ meta-analyses show, what happens at the extremes of the ability range, and why mixed-handedness may matter more than which hand you write with.
How common left-handedness is
About one person in ten is left-handed. A 2020 meta-analysis in Psychological Bulletin by Marietta Papadatou-Pastou and colleagues put the best overall estimate at 10.6%. The figure ranged from 9.3% under the strictest definition of left-handedness to 18.1% under the loosest definition, which counts everyone who is not consistently right-handed. How handedness is measured, by writing hand alone or by a questionnaire covering many tasks, changes the answer.
Men are a little more likely than women to be left-handed. An earlier meta-analysis of 144 studies and almost 1.8 million people found a male-to-female odds ratio of 1.23. The 2020 meta-analysis also found that rates vary with ancestry and with the year a study was published, and its authors pointed to cultural pressure against using the left hand as one reason.
Genes explain only part of the picture. In a study of 54,270 Australian and Dutch twins and their siblings, Medland and colleagues estimated that additive genetic effects accounted for about a quarter (23.6%) of the variation in handedness, with the rest due to environmental influences unique to each person. A genome-wide study of more than 1.7 million people by Cuellar-Partida and colleagues found 41 genetic variants linked to left-handedness and 7 linked to ambidexterity, with a low genetic correlation between the two. That last finding suggests that being left-handed and being mixed-handed are largely different traits, which matters for the IQ research below.
What the IQ research shows
The key study is a 2018 systematic review and meta-analysis by Eleni Ntolka and Marietta Papadatou-Pastou, titled bluntly "Right-handers have negligibly higher IQ scores than left-handers". They reviewed 36 studies with 66,108 people that had measured full-scale IQ by handedness group, and most of those studies found no difference between left- and right-handers. Eighteen studies, with 20,442 people, had enough data to combine.
The pooled results were:
• Left-handers versus right-handers: a statistically significant but marginal difference favouring right-handers, d = -0.07. On the IQ scale, where one standard deviation is 15 points, that is about one point.
• Robustness: the difference was no longer significant when the largest study was excluded.
• Non-right-handers and mixed-handers versus right-handers: no difference in mean IQ.
• Sex: no difference between men and women in the pattern.
A one-point gap between group averages is far smaller than the measurement error of any individual IQ score. Knowing someone's writing hand tells you essentially nothing about their IQ.
Studies of specific abilities find similarly small effects. A meta-analysis by Somers and colleagues pooled 14 studies (359,890 people) on verbal ability and 16 studies (218,351 people) on spatial ability. Left- and right-handers did not differ in verbal ability overall, although right-handed children showed a small advantage. There was a modest advantage for right-handers in spatial ability, mostly on mental rotation tasks, one of the item types discussed in our article on visual-spatial reasoning and why it shows up on an IQ test.
Some large child cohorts have found a slightly bigger gap. Johnston and colleagues, using a nationally representative sample of young children, found that left-handed and mixed-handed children scored significantly lower on nearly all measures of development, more so for boys, and that family income and parenting differences did not explain the gap. Nicholls, Johnston and Shields analysed about 10,000 children in the British Cohort Study and also linked left-handedness to slightly lower cognitive ability. Birth complications in that sample predicted lower ability but did not predict handedness, which argues against the old idea that left-handedness is mainly a sign of early brain injury.
The extremes: intellectual disability and giftedness
Left-handedness is more common at the low end of the ability range. In a set of meta-analyses covering 16,076 people, Papadatou-Pastou and Tomprou compared handedness in 5,795 people with intellectual disability of unknown cause, 8,312 typically developing people and 1,969 intellectually gifted people. Raised rates of atypical handedness were robust only in the intellectual disability group. Our page on low IQ and intellectual disability explains how that diagnosis is made. A higher rate of left-handedness in a clinical group does not mean left-handers in general have lower IQs, because most left-handers are not in that group.
The high end is less clear. In 1986 Camilla Benbow reported that left- or mixed-handedness was unusually frequent among extremely precocious students who scored in the top 1 in 10,000 for mathematical or verbal reasoning. That finding fed the popular belief that left-handers are overrepresented among the gifted, but the later meta-analysis did not find a robust handedness difference between gifted and typically developing groups.
Mixed-handedness and the brain
Several studies suggest that how strongly someone prefers one hand may matter more than which hand it is. In the UK's National Child Development Study, Crow and colleagues measured relative hand skill in 12,770 children at age 11 with a square-checking task. The largest deficits in verbal, non-verbal and mathematical ability appeared close to the point of equal skill in both hands, which the authors called "hemispheric indecision", with only modest decrements in extreme right-handers. A later reanalysis of the same cohort by Cheyne and colleagues found lower reading and maths scores in children who wrote with one hand but were more skilled with the other.
Corballis, Hattie and Fletcher found the same pattern in adults who took an IQ test as part of a television programme: people who said they wrote with either hand scored lower than both left- and right-handers. The Ntolka meta-analysis found no mean IQ difference for mixed-handers, so the evidence is mixed, and mixed-handedness is defined differently from study to study.
Handedness is linked to how the brain organises language. Knecht and colleagues measured language lateralisation in 326 healthy adults and found that right-hemisphere dominance for language rose from 4% in strong right-handers to 15% in ambidextrous people and 27% in strong left-handers. Most left-handers, in other words, still process language mainly in the left hemisphere. None of this means that left-handers are "right-brained" thinkers, an idea our article on whether you are left-brained or right-brained examines separately. Handedness itself needs no assessment or correction. If a child is struggling at school, whatever their writing hand, an educational psychologist can assess the reasons.
Frequently asked questions
Do left-handed people have a higher IQ?
No. The largest meta-analysis found that right-handers scored about one point higher on average, which the authors described as negligible.
What is the average IQ of left-handed people?
Left-handers average about the same as everyone else, close to 100 on a standard IQ scale. The group difference from right-handers is around one point.
Are left-handers more likely to be geniuses?
There is no good evidence for this. One 1986 study found more left- and mixed-handedness among extremely precocious students, but a later meta-analysis did not find a robust handedness difference in gifted groups.
Is being ambidextrous linked to lower IQ?
Some large studies found slightly lower scores in people with roughly equal skill in both hands, but the main IQ meta-analysis found no difference for mixed-handers. The evidence is inconsistent.
What percentage of people are left-handed?
About 10.6%, according to a 2020 meta-analysis, with estimates from 9.3% to 18.1% depending on how left-handedness is defined.
The takeaway
Left handed IQ research gives a clear answer: the average difference between left- and right-handers is about one IQ point, too small to matter for any individual. Left-handedness is somewhat more common among people with intellectual disability, and some studies find slightly lower scores in people with no clear hand preference, but most left-handers score just like everyone else. Your writing hand will not tell you much about your reasoning ability, while a professionally developed IQ test can.
References
1. Papadatou-Pastou, M., Ntolka, E., Schmitz, J., Martin, M., Munafò, M. R., Ocklenburg, S., & Paracchini, S. (2020). Human handedness: A meta-analysis. Psychological Bulletin, 146(6), 481-524. doi.org
2. Papadatou-Pastou, M., Martin, M., Munafò, M. R., & Jones, G. V. (2008). Sex differences in left-handedness: A meta-analysis of 144 studies. Psychological Bulletin, 134(5), 677-699. doi.org
3. Medland, S. E., Duffy, D. L., Wright, M. J., Geffen, G. M., Hay, D. A., Levy, F., ... Boomsma, D. I. (2009). Genetic influences on handedness: Data from 25,732 Australian and Dutch twin families. Neuropsychologia, 47(2), 330-337. doi.org
4. Cuellar-Partida, G., Tung, J. Y., Eriksson, N., Albrecht, E., Aliev, F., Andreassen, O. A., ... Medland, S. E. (2021). Genome-wide association study identifies 48 common genetic variants associated with handedness. Nature Human Behaviour, 5(1), 59-70. doi.org
5. Ntolka, E., & Papadatou-Pastou, M. (2018). Right-handers have negligibly higher IQ scores than left-handers: Systematic review and meta-analyses. Neuroscience and Biobehavioral Reviews, 84, 376-393. doi.org
6. Somers, M., Shields, L. S., Boks, M. P., Kahn, R. S., & Sommer, I. E. (2015). Cognitive benefits of right-handedness: A meta-analysis. Neuroscience and Biobehavioral Reviews, 51, 48-63. doi.org
7. Johnston, D. W., Nicholls, M. E. R., Shah, M., & Shields, M. A. (2009). Nature's experiment? Handedness and early childhood development. Demography, 46(2), 281-301. doi.org
8. Nicholls, M. E. R., Johnston, D. W., & Shields, M. A. (2012). Adverse birth factors predict cognitive ability, but not hand preference. Neuropsychology, 26(5), 578-587. doi.org
9. Papadatou-Pastou, M., & Tomprou, D.-M. (2015). Intelligence and handedness: Meta-analyses of studies on intellectually disabled, typically developing, and gifted individuals. Neuroscience and Biobehavioral Reviews, 56, 151-165. doi.org
10. Benbow, C. P. (1986). Physiological correlates of extreme intellectual precocity. Neuropsychologia, 24(5), 719-725. doi.org
11. Crow, T. J., Crow, L. R., Done, D. J., & Leask, S. (1998). Relative hand skill predicts academic ability: Global deficits at the point of hemispheric indecision. Neuropsychologia, 36(12), 1275-1282. doi.org
12. Cheyne, C. P., Roberts, N., Crow, T. J., Leask, S. J., & García-Fiñana, M. (2010). The effect of handedness on academic ability: A multivariate linear mixed model approach. Laterality, 15(4), 451-464. doi.org
13. Corballis, M. C., Hattie, J., & Fletcher, R. (2008). Handedness and intellectual achievement: An even-handed look. Neuropsychologia, 46(1), 374-378. doi.org
14. Knecht, S., Dräger, B., Deppe, M., Bobe, L., Lohmann, H., Flöel, A., Ringelstein, E.-B., & Henningsen, H. (2000). Handedness and hemispheric language dominance in healthy humans. Brain, 123(12), 2512-2518. doi.org
Hero image: Left-handed writing with wristwatch, by Alejandro Escamilla, licensed CC0 (creativecommons.org/publicdomain/zero/1.0/deed.en). Via Wikimedia Commons.
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