On Correlation (1900-1949)

"It had appeared from observation, and it was fully confirmed by this theory, that such a thing existed as an 'Index of Correlation', that is to say, a fraction, now commonly written T, that connects with close approximation every value of the deviation on the part of the subject, with the average of all the associated deviations of the Relative [...]" (Francis Galton, "Memories of My Life", 1908)

"The whole world appears resolved into such world-lines. And I should like to say beforehand that, according to my opinion, it would be possible for the physical laws to find their fullest expression as correlations of these world-lines." (Hermann Minkowski, "Space and Time" ["Raum und Zeit"], [Address to the 80th Assembly of German Natural Scientists and Physicians] 1908)

"One of the main duties of science is the correlation of phenomena, apparently disconnected and even contradictory." (Frederick Soddy, "The Interpretation of Radium and the Structure of the Atom", 1909)

"To speak of the cause of an event is therefore misleading. Any set of antecedents from which the event can theoretically be inferred by means of correlations might be called a cause of the event. But to speak of the cause is to imply a uniqueness [...]." (Bertrand Russell, "Mysticism and Logic: And Other Essays", 1910)

"'Correlation' is a term used to express the relation which exists between two series or groups of data where there is a causal connection. In order to have correlation it is not enough that the two sets of data should both increase or decrease simultaneously. For correlation it is necessary that one set of facts should have some definite causal dependence upon the other set [...]" (Willard C Brinton, "Graphic Methods for Presenting Facts", 1919)

"One of the main duties of science is the correlation of phenomena, apparently disconnected and even contradictory." (Frederick Soddy, "Structure of the Atom", 1920)

"'Causation' has been popularly used to express the condition of association, when applied to natural phenomena. There is no philosophical basis for giving it a wider meaning than partial or absolute association. In no case has it been proved that there is an inherent necessity in the laws of nature. Causation is correlation. [...] perfect correlation, when based upon sufficient experience, is causation in the scientific sense." (Henry E Niles, "Correlation, Causation and Wright's Theory of 'Path Coefficients'", Genetics, 1922)

"The correlation table is useful for three distinct purposes. It affords a valuable visual -representation of the whole of the observations, which with a little experience is as easy to comprehend as a dot diagram; it serves as a compact record of extensive data, which, as far as the two variates are concerned, is complete. […] the data so presented form a convenient basis for the immediate application of methods of statistical reduction. The most important statistics which the data provide, means, variances, and covariance, can be most readily calculated from the correlation table." (Sir Ronald A Fisher, "Statistical Methods for Research Workers", 1925)

"The futile elaboration of innumerable measures of correlation, and the evasion of the real difficulties of sampling problems under cover of a contempt for small samples, were obviously beginning to make its pretensions ridiculous. These procedures were not only ill-aimed, but for all their elaboration, not sufficiently accurate." (Sir Ronald A Fisher, "Statistical Methods for Research Workers", 1925)

"When the relationship is of a quantitative nature, the appropriate statistical tool for discovering and measuring the relationship and expressing it in a brief formula is known as correlation." (Frederick E Croxton & Dudley J Cowden, "Practical Business Statistics", 1937)

"Graphic methods are very commonly used in business correlation problems. On the whole, carefully handled and skillfully interpreted graphs have certain advantages over mathematical methods of determining correlation in the usual business problems. The elements of judgment and special knowledge of conditions can be more easily introduced in studying correlation graphically. Mathematical correlation is often much too rigid for the data at hand." (John R Riggleman & Ira N Frisbee, "Business Statistics", 1938)

"[…] statistical literacy. That is, the ability to read diagrams and maps; a 'consumer' understanding of common statistical terms, as average, percent, dispersion, correlation, and index number."  (Douglas Scates, "Statistics: The Mathematics for Social Problems", 1943)