In 1835 Belgian statistician and astronomer Lambert Quételet suggested applying statistical probabilities to quantitative trait differences between individuals. The resulting Bell Curve, a bilateral graphic with tails resembling a bell's rim, served to compare individual characteristics against those of a group. In 1869 Francis Galton (supporter of Darwin's evolutionary theory) extended the meaning of the graph to include the measurement of natural ability in addition to other traits. It reflects distributions of most normally developed human physical, intellectual, and personality traits, designating a probable frequency for each value of the trait. The average of a set of values becomes the distribution mean, located midpoint in this graphic. Valuable in psychological testing, comparing individuals' abilities relative to others may suggest relevant outcomes such as need for special educational treatment. Some genetics-oriented researchers have generated controversy by applying Bell Curves to intelligence data collected on racial groups. Questionable assumptions about intellectual inferiority among some races leads to flawed educational treatments, impeding ability development for specific groups.
Anastasi, Anne. Psychological Testing, 5th edition. New York:Macmillan, 1982.
Herrnstein, Richard J., and Charles Murray. The Bell Curve: Intelligence and Class Structure in American Life. New York: Free Press, 1994.