Francis Galton : biography
He also discovered the properties of the bivariate normal distribution and its relationship to regression analysis.
Correlation and regression
After examining forearm and height measurements, Galton introduced the concept of correlation in 1888 . Correlation is the term used by Aristotle in his studies of animal classification, and later and most notably by Georges Cuvier in Histoire des progrès des sciences naturelles depuis 1789 jusqu’à ce jour (5 volumes, 1826–1836). Correlation originated in the study of correspondence as described in the study of morphology. See R.S. Russell, Form and Function. He was not the first to describe the mathematical relationship represented by the correlation coefficient, but he rediscovered this relationship and demonstrated its application in the study of heredity, anthropology, and psychology. Galton’s later statistical study of the probability of extinction of surnames led to the concept of Galton–Watson stochastic processes . This is now a core of modern statistics and regression.
Galton invented the use of the regression line , and was the first to describe and explain the common phenomenon of regression toward the mean, which he first observed in his experiments on the size of the seeds of successive generations of sweet peas. He is responsible for the choice of r (for reversion or regression) to represent the correlation coefficient. In the 1870s and 1880s he was a pioneer in the use of normal distribution to fit histograms of actual tabulated data.
Theories of perception
Galton went beyond measurement and summary to attempt to explain the phenomena he observed. Among such developments, he proposed an early theory of ranges of sound and hearing, and collected large quantities of anthropometric data from the public through his popular and long-running Anthropometric Laboratory, which he established in 1884 where he studied over 9,000 people.Gillham, Nicholas Wright (2001). A Life of Sir Francis Galton: From African Exploration to the Birth of Eugenics, Oxford University Press. ISBN 0-19-514365-5. It was not until 1985 that these data were analyzed in their entirety.
Galton’s study of human abilities ultimately led to the foundation of differential psychology and the formulation of the first mental tests. He was interested in measuring humans in every way possible. This included measuring their ability to make sensory discrimination which he assumed was linked to intellectual prowess. Galton suggested that individual diﬀerences in general ability are reﬂected in performance on relatively simple sensory capacities and in speed of reaction to a stimulus, variables that could be objectively measured by tests of sensory discrimination and reaction time. He also measured how quickly people reacted which he later linked to internal wiring which ultimately limited intelligence ability. Throughout his research Galton assumed that people who reacted faster were more intelligent than others.
Galton also devised a technique called composite portraiture" (produced by superimposing multiple photographic portraits of individuals’ faces registered on their eyes) to create an average face. (See averageness). In the 1990’s, a hundred years after his discovery, much psychological research has examined the attractiveness of these faces, an aspect that Galton had remarked on in his original lecture. Others, including Sigmund Freud in his work on dreams, picked up Galton’s suggestion that these composites might represent a useful metaphor for an Ideal type or a concept of a “natural kind" (see Eleanor Rosch) — such as Jewish men, criminals, patients with tuberculosis, etc. — onto the same photographic plate, thereby yielding a blended whole, or “composite”), that he hoped could generalize the facial appearance of his subject into an “average” or “central type.”.Galton, F. (1878). Journal of the Anthropological Institute of Great Britain and Ireland, 8, 132–142. See also entry Modern physiognomy under Physiognomy).