European scientists conducted a large-scale meta-analysis of works devoted to the leading hand of the man, and more accurately estimate the number of left-handers. The average for all the considered studies (nearly 2.4 million participants) left-handers turned out to be 10.6 per cent, although this figure is, depending on the work ranged from 9.3 to 18.1%. Article published in the journal Psychological Bulletin.
The human brain is divided into two parts: despite the fact that outwardly they seem to be identical, they are functionally asymmetric. For example, for it to answer areas of the frontal and temporal lobes of the left hemisphere, but the corresponding areas of the right hemisphere — is no more. That’s why people who suffered a stroke in the left hemisphere, there were serious disorders of language (aphasia) — compared to those who have in the course of the stroke affected the right hemisphere.
For the right and left part of our body also meet different hemisphere: for the left hand meets the right hemisphere, and for the movement of the right and the left. Due to the fact that the brain is functionally asymmetrical, asymmetrically work and body — so get righties and lefties (more details about this you can read in our material).
Right-handers in the world, the vast majority (about 90 percent), but their assessment is inaccurate, largely due to the fact that different studies, conducting the counting, use different techniques. In addition, they rarely take into account the number Ambidextrous (those who for different tasks can use both left and right hand) and focus only on one task — writing.
Marietta Papadatou Paste (Marietta Papadatou-Pastou) of the Athens national Kapodistrian University and her colleagues decided to verify the number of righties and lefties in the world using meta-analysis: the sample for all studies have got 2396170 persons 16 years and older with different levels of education and from different countries. The studies used different methodologies to test dominant hand, but in General the authors of the meta-analysis focused on preferences of research participants to the use of a particular hand.
The number of left-handers from all study participants ranged from 9.3 percent if the criteria for the selection of left-handers was the most restrictive (that is, the number of left-handers who use left hand for everything), to 18.1 percent (the number of left-handers who use left hand to perform at least some tasks). The average number of left-handers in all studies was equal to 10.6 per cent and 10.4 per cent, if we exclude studies that addressed the preference for leading professional athletes.
The percentage of left-handers from study to study dependent, on the one hand, from the studies selected in this methodology (and the year of publication of the article), and with another — the age and origin of the participants. This is understandable: the desire to reduce the number of left-handers is strongly dependent on the cultural characteristics of each population, and also it changes over time. For example, in the Soviet Union prior to the adoption of appropriate laws prohibiting of left-handed children were forcibly retrained in schools and at home.
In addition to the most accurate to date, counting the left-handers, the researchers also point to the importance of the methodology used in such studies: according to them, the problem with the calculations of left-handers in the world is that studies use different formats of assessment, on the one hand, and with another — does not always take into account important side variables like cultural differences.
Of course, functional naturalnosti limbs — not exclusively human feature: asymmetry of the nervous system that it determines is inherent in most living organisms (of course, we are talking about those organisms that have a nervous system exists at all). So, lefties and righties, for example, among the bees: they have individual tendency to select right or left side during the flight.