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Summary Article: Pearson, Karl (1857-1936)
From The Hutchinson Dictionary of Scientific Biography

Place: United States of America

Subject: biography, maths and statistics

English mathematician and biometrician who is chiefly remembered for his crucial role in the development of statistics as applied to a wide variety of scientific and social topics.

Pearson was born in London on 27 March 1857. He was tutored at home, except for a period 1866-73 when he attended University College School. He began his university studies at King's College, Cambridge, in 1875, where an indication of Pearson's somewhat uncompromising and unconventional spirit is found in his successful pressuring of the authorities to abolish the mandatory classes in divinity for undergraduates. Pearson graduated with high honours in 1879, and was awarded a fellowship of the college 1880-86 that gave him financial independence without obligation and enabled him to travel and study as he pleased. He visited universities in Germany, took a degree in law in 1881 (although he never practised), and was awarded his master's degree in 1882. In 1884 - still officially a fellow of King's College - Pearson was named Goldsmid Professor of Applied Mathematics and Mechanics at University College, London; he was to hold this post until 1911 although his most productive work during the period was carried out elsewhere. He was also appointed lecturer in geometry at Gresham College, London, in 1891, which required him to give a short series of lectures each year. It was from them on that Pearson became interested in the development of statistical methods for the investigation of evolution and heredity. His efforts in this aim were most fruitful, and were recognized by his election as fellow of the Royal Society in 1896 (which awarded him its Darwin Medal in 1898). He then founded and became editor (until his death) of Biometrika, a journal established to publish work on statistics as applied to biological subjects. His work on eugenics led to his appointment as head of the Laboratory of Eugenics at London University upon Francis Galton's retirement in 1906. In 1911 he became the first Galton Professor of Eugenics, a post he retained until 1933, when he retired to become emeritus professor. (His department was then split into two sections, one of which was headed by Pearson's son.) Pearson continued to work in his department until his death in Coldharbour, Surrey, on 27 April 1936.

During the early years of Pearson's career he did little work in mathematics, concentrating instead on law and political issues. His appointment to the Goldsmid Chair required him to focus his attentions on academic duties and on writing. A further marked change overtook his life in the early 1890s with the publication of Francis Galton's book Natural Inheritance, and with Pearson's exposure to the ideas of Walter Weldon, the newly appointed professor of zoology at University College.

Weldon was interested in the application of Galton's methods for correlation and regression to the investigation of the validity of Charles Darwin's model of natural selection. Pearson threw himself into this project with great vigour, examining graphical methods for data presentation, studying probability theory and concepts such as standard deviation (a term he himself introduced in 1893, although the idea was by then nearly a century old), and more complex distribution patterns. He submitted many papers on statistical methods to the Royal Society of London, but encountered some stiff opposition to his mathematical approach to biological material. It was this that prompted him to launch his own journal, Biometrika.

Early in his investigation he determined a method for finding values for the parameters required to describe a particular distribution. Another major achievement was his classification of the different types of curves produced in the plotting of data into general types. This contributed to putting the Gaussian (or ‘normal’) distribution into more realistic perspective.

Pearson's discoveries included the Pearson coefficient of correlation (1892), the theory of multiple and partial correlation (1896), the coefficient of variation (1898), work on errors of judgement (1902), and the theory of random walk (1905). The last theory has since been applied to the study of random processes in many fields. In addition, Pearson's Biometrika for 1901 is a book of tables of the ordinates, integrals, and other properties of Pearson's curves, and was of great practical use in making statistical methods accessible to a large number of scientists.

Perhaps the most familiar of Pearson's achievements was his discovery in 1900 of the χ2 (chi-squared) test applied to determine whether a set of observed data deviates significantly from what would have been predicted by a ‘null hypothesis’ (that is, totally at random). Pearson also demonstrated that it could be applied to examine whether two hereditary characteristics (such as height and hair colour) were inherited independently.

Weldon's death in 1906 dealt a severe blow to Pearson's work in the field of mathematics as applied to biology; Pearson himself lacked the biological background to keep up with the increasingly sophisticated developments in the field of genetics. A great controversy had grown up around the approach of Weldon - who believed in gradual but continuous evolution - as against that of the followers of Gregor Mendel, such as William Bateson - who believed in intermittent variation. Pearson felt that Mendel's results were not incompatible with a statistical approach, although many Mendelians were convinced that they were. But it was the equally celebrated statistician Ronald Fisher who was ultimately able to bring about the beginnings of a reconciliation between the two approaches.

During the rest of Pearson's career he concentrated on the establishment of a thriving department dedicated to the training of postgraduate students so that statistical techniques might be applied to subjects in many areas of academic study. He also worked on eugenics, examining the relative importance of environment and heredity in disorders such as tuberculosis and alcoholism, and in the incidence of infant mortality.

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