“The Proof and Measurement of Association between Two Things”, 1904 (; backlinks; similar):
[Attempted to study the scientific correlation between 2 things. Any correlational experiment can only be regarded as a sample and presents a certain amount of accidental deviation from the real general tendency. Accidental deviation can be measured by the ‘probable error’. Accidental deviation depends on the number or cases, and on the largeness of existing correspondence. Probable error varies according to the method of calculation. While the number of Subjects helps to reduce accidental deviation, it has no effect upon systematic deviation, except that it indirectly leads to an augmentation. Therefore, the number of cases should be determined by the principle that the measurements to be aggregated together should have their error brought to the same general order of magnitude. Suggests that probable errors must be kept down to limits small enough for the particular object of investigation to be proved.
Early in the 20th century, Spearman published several articles in the American Journal of Psychology on experimental methodology in general and the method of correlation in particular. They are all-important and seminal works. The following article, “The proof and measurement of association between 2 things”, is important because Spearman published it as “a commencement at attempting to remedy” a problem in the experimentation of his day in which “laborious series of experiments are executed and published with the purpose of demonstrating some connection between 2 events” but in which experimental importance is not ascertainable.
This article is Spearman’s explication of the adaptation of Pearson’s product-moment correlation statistic to experimental results in psychology. It should be noted that Spearman made an error in his correlation formula on page 77. He defines x and y as medians rather than means. He caught it himself and made the correction in a later article.
It is hard to calculate the impact of Spearman’s article on modern psychology except to say that it has been immense.]
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