American psychologist who was instrumental in the development of psychometrics (psychological testing), the science that measures mental functions, and who developed statistical techniques for multiple-factor analysis of performance on psychological tests.

Thurstone was originally interested in mathematics and engineering. He studied electrical engineering at Cornell University, Ithaca, New York, and worked briefly as an assistant to Thomas Edison before taking a teaching post at the University of Minnesota in Minneapolis (1912). He became interested in the psychology of learning and received his Ph.D. in psychology from the University of Chicago in 1917. He held a position as chairman of the department of psychology at the Carnegie Institute of Technology until 1924, when he returned to the University of Chicago as associate professor of psychology and became a full professor three years later. In 28 years at the University of Chicago, he established the Psychometric Laboratory there, helped found the Psychometric Society, and produced many important articles and books.

Thurstone was especially concerned with the measurement of people's attitudes and intelligence (intelligence, human). His criticisms of existing testing methods appeared in The Reliability and Validity of Tests (1931). He attacked the concept of an ideal mental age, then commonly used in intelligence testing, advocating instead the use of percentile rankings to compare performance. He also developed a rating scale for locating individual attitudes and opinions along a continuum between extremes.

His principal work, The Vectors of Mind (1935), presented Thurstone's method of factor analysis to explain correlations between results in psychological tests. Thurstone rejected the idea that any one factor had more general application than others and evaluated all factors influencing performance on a given test at one time, devising new statistical techniques to perform the factor analysis. His studies of intelligence using these techniques led to the Primary Mental Abilities Test (1938), which measured components of human intelligence such as reasoning ability, word fluency, verbal comprehension, facility with numbers, spatial visualization, and rote memory. Multiple-Factor Analysis (1947), his other major work, was an extensive rewriting of Vectors.

In 1952 Thurstone moved his laboratory for psychological measurement from Chicago to the University of North Carolina, Chapel Hill, where he served as professor of psychology until his death.