Correlation
Galton also introduced the idea of ‘co-relation’ (Galton,1888), or correlation, which is a measure of the extent to which two variables, such asweight and height, are related.A correlation of +1 would reflect a perfect positive relationship between the two variables –
as height increases, so weight increases in direct proportion. But we know from our own xperience that there is not necessarily a perfect relationship (there are some short, heavy-set people andsome tall, skinny people) so the correlation between weight and height is ikely to be less than one but still positive. A correlationof –1 would reveal a perfect negative relationship, where an increase in scores on one variable is directly related to decreasing scores on the other – for example, the number of cigarettes smoked is negatively correlated with life expectancy. Together, the notions of normal distribution and correlation allow us to consider how our abilities vary in relation to each other and in relation to the abilities of others in the population, and how well we can use scores on one variable to predict scores on another.Early attempts to measure intelligence In his Anthropometric Laboratory in London in the late nineteenth century, Galton attempted to measure a range of attributes that show individual variation. These included physical attributes such as head circumference, height and hand size, as well as intellectual characteristics (which, remember, he believed were a function of neural processes). These intellectual measures included basic sensory-motor tasks, such as speed of reaction to sounds and visual stimuli. Galton then compared these innovative measures of ‘intelligence’ to subjective estimates of the intellectual prowess of his participants based on their ‘reputation’ and eminence in the family tree (There were no such things as intelligence tests at the time!). Unfortunately, his empirical efforts were not successful.
Subsequently, Charles Spearman (1904) set out to estimate the intelligence of 24 children in his village school. He discovered a relationship between each child’s performance in a number of domains (including teachers’ ratings of ‘cleverness’ and ratings by other students of their ‘common sense out of school’) and measures of their ability to discriminate light, weight and pitch. In other studies, he found strong associations between scores on examinations in different subject areas such as classics and maths. Linking together these strands of evidence, Spearman concluded that there was a ‘general’ intelligence underlying performance on these very different tasks. He regarded general intelligence, or g, as a unitary, biological and inherited determinant of measurable
intellectual differences. In apparent contradiction, Spearman also noted that there were some ‘specific abilities’, such as musical aptitude, that contributed to differentially exceptional performance in specific areas and seemed less related to performance in other disciplines. But his finding of a general feature that underlies performance in many areas was so radical that it became the hallmark of his work. Spearman likened g to mental energy – a limited resource available to all intellectual tasks. So the idea was that individuals differ in general intelligence because they have different amounts of this mental energy.
Galton also introduced the idea of ‘co-relation’ (Galton,1888), or correlation, which is a measure of the extent to which two variables, such asweight and height, are related.A correlation of +1 would reflect a perfect positive relationship between the two variables –
as height increases, so weight increases in direct proportion. But we know from our own xperience that there is not necessarily a perfect relationship (there are some short, heavy-set people andsome tall, skinny people) so the correlation between weight and height is ikely to be less than one but still positive. A correlationof –1 would reveal a perfect negative relationship, where an increase in scores on one variable is directly related to decreasing scores on the other – for example, the number of cigarettes smoked is negatively correlated with life expectancy. Together, the notions of normal distribution and correlation allow us to consider how our abilities vary in relation to each other and in relation to the abilities of others in the population, and how well we can use scores on one variable to predict scores on another.Early attempts to measure intelligence In his Anthropometric Laboratory in London in the late nineteenth century, Galton attempted to measure a range of attributes that show individual variation. These included physical attributes such as head circumference, height and hand size, as well as intellectual characteristics (which, remember, he believed were a function of neural processes). These intellectual measures included basic sensory-motor tasks, such as speed of reaction to sounds and visual stimuli. Galton then compared these innovative measures of ‘intelligence’ to subjective estimates of the intellectual prowess of his participants based on their ‘reputation’ and eminence in the family tree (There were no such things as intelligence tests at the time!). Unfortunately, his empirical efforts were not successful.
Subsequently, Charles Spearman (1904) set out to estimate the intelligence of 24 children in his village school. He discovered a relationship between each child’s performance in a number of domains (including teachers’ ratings of ‘cleverness’ and ratings by other students of their ‘common sense out of school’) and measures of their ability to discriminate light, weight and pitch. In other studies, he found strong associations between scores on examinations in different subject areas such as classics and maths. Linking together these strands of evidence, Spearman concluded that there was a ‘general’ intelligence underlying performance on these very different tasks. He regarded general intelligence, or g, as a unitary, biological and inherited determinant of measurable
intellectual differences. In apparent contradiction, Spearman also noted that there were some ‘specific abilities’, such as musical aptitude, that contributed to differentially exceptional performance in specific areas and seemed less related to performance in other disciplines. But his finding of a general feature that underlies performance in many areas was so radical that it became the hallmark of his work. Spearman likened g to mental energy – a limited resource available to all intellectual tasks. So the idea was that individuals differ in general intelligence because they have different amounts of this mental energy.
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