# Karl Pearson1857–1936

Neuroscience is dependent upon statistical procedures for evaluating the benefits of experimental interventions. Galton initiated this movement, but it was pursued with greater mathematical precision by Pearson He laid the foundations for modern statistics. He explored the mathematical basis for correlation, expressing the relationship between two variables by a single coefficient, and he established a test for the goodness-of-fit between observed and theoretical distributions (chi-square). He was a mathematician who applied his skills to the domain of biology, and was one of the original biometricians. His aim was to enlist statistical studies of variation to support the Darwinian theory of evolution. In 1898 he was awarded the Darwin Medal by the Royal Society of London, of which he was a fellow. Philosophically he was a positivist in the mould of Hume and Mach (indeed, Mach’s *Analysis of Sensations* is dedicated to Pearson), believing that causation was correlation in time. His philosophy was expressed in *The Grammar of Science* (1892): “The classification of facts, the recognition of their sequence and their relative significance is the function of science, and the habit of forming a judgment upon these facts unbiassed by personal feeling is the characteristic of what may be termed the scientific frame of mind.. The unity of all science consists alone in its method, not in its material.” Galton encouraged Pearson in his biometrical endeavours, and in 1896 the latter derived a more convenient formulation for computing the former’s correlation, which was denoted by *r*. Pearson referred to *r* as the Galton function or coefficient of correlation, but it is now called the product-moment correlation coefficient. The journal *Biometrika* was founded by Galton and Pearson in 1901 and Pearson edited it. Pearson was Galton’s biographer. Pearson was born in London and studied mathematics at Cambridge University; Maxwell was one of his teachers. He then went to Germany, where he indulged his eclectic interests attending lectures ranging from physics to metaphysics. His love of German science and literature was perhaps the basis for his adoption of the Germanic Karl in preference to his given name Carl. On his return to England he studied law but never practiced it. He was appointed professor of applied mathematics and mechanics at University College, London in 1884, and his most influential work in statistics was conducted in the decade that spans the turn of the century. It was inspired both by the publication of Galton’s *Natural Inheritance* (1889) and by his zoologist colleague Walter Frank Raphael Weldon (1860-1906). In 1911 a bequest from Galton endowed a chair of eugenics at the University of London with the request that it first be offered to Pearson, who accepted it. This continued a link between biometrics and eugenics that was initiated by Galton’s *Hereditary Genius* and would be extended by Fisher, though Pearson and Fisher became bitter rivals. Pearson is here defined graphically by the letter *r* representing the product-moment coefficient of correlation that results from applying his procedures. His rueful prediction that he would be remembered mainly by a symbol or an equation proved correct.