![]() ![]() ![]() To use decile to mean tenth – as when, for example, speaking of students “in the top decile” (according to their examination marks) – is not only pompous but also wrong and means that yet another word will eventually have to be invented to perform the function that Galton created decile to fulfil. There are, pretty obviously, ten tenths of a distribution, but there are, slightly less obviously, only nine deciles, since the deciles are the boundaries between the tenths. Of course, words have a way of developing a life of their own, so that, unfortunately decile is increasingly being applied to mean tenth. For example, correlation and deviate are due to him, as is regression, and he was the originator of terms and concepts such as quartile, decile and percentile, and of the use of median as the midpoint of a distribution 2. Many words in our statistical lexicon were coined by Galton. ![]() Galton was a brilliant natural statistician. In fact he subsequently freely acknowledged his weakness in formal mathematics, but this weakness was compensated by an exceptional ability to understand the meaning of data. He dabbled in medicine and then read mathematics at Cambridge, but eventually had to take a pass degree. Galton's later progress in education was not quite so smooth. And before you get too impressed, his birthday was February 16th so he was very nearly five! Apparently Galton was also a truthful child, since, having written the letter, he had realised that what he had claimed about the numbers 9 and 11 was not quite true and had tried to obliterate them. ![]()
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