Normal distribution
Another of Galton’s contributions was to bring statistical understandings from the physical sciences to the study of psychology – particularly, the notion of normal distribution. Galton noted that for any of our ‘natural gifts’ (physical, temperamentalor intellectual) there will be an ‘average’ amount of that feature, to which most people approximate. Then, as we consider scores increasingly higher or increasingly lower than that ‘average score’, there will be fewer and fewer people registering those scores. Galton explains it as follows:Suppose a million of the men . . . stand in turns, with their backs against a vertical board of sufficient height, and their heights to be dotted off upon it . . . The line of average height is that which divides the dots into two equal parts . . . The dots will be found to be ranged so symmetrically on either side of the line of average,that the lower half of the diagram will be almost a precise reflection of the upper. (1892, 27–8)The idea here was that, in this group, there would be many men of about average height (say 160cm) and increasingly fewer men as we approach 190cm, and similarly fewer as we approach 130cm.Studying the normal distribution of psychological characteristicssuch as intelligence enables us to estimate attributes withina group and to have a point of comparison for an individual’s abilities. So, we expect that most people will approximate average intelligence, and there will be a small but predictable number of people of exceptionally high intelligence and an equally small and predictable number will be severely mentally disabled.
Another of Galton’s contributions was to bring statistical understandings from the physical sciences to the study of psychology – particularly, the notion of normal distribution. Galton noted that for any of our ‘natural gifts’ (physical, temperamentalor intellectual) there will be an ‘average’ amount of that feature, to which most people approximate. Then, as we consider scores increasingly higher or increasingly lower than that ‘average score’, there will be fewer and fewer people registering those scores. Galton explains it as follows:Suppose a million of the men . . . stand in turns, with their backs against a vertical board of sufficient height, and their heights to be dotted off upon it . . . The line of average height is that which divides the dots into two equal parts . . . The dots will be found to be ranged so symmetrically on either side of the line of average,that the lower half of the diagram will be almost a precise reflection of the upper. (1892, 27–8)The idea here was that, in this group, there would be many men of about average height (say 160cm) and increasingly fewer men as we approach 190cm, and similarly fewer as we approach 130cm.Studying the normal distribution of psychological characteristicssuch as intelligence enables us to estimate attributes withina group and to have a point of comparison for an individual’s abilities. So, we expect that most people will approximate average intelligence, and there will be a small but predictable number of people of exceptionally high intelligence and an equally small and predictable number will be severely mentally disabled.
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