Marked the start of testing and measurement of complex psychological qualities.
Francis Galton (1822-1911) Invented intelligence tests, studied inheritence and nurture of mental characteristics; invented scatterplots and correlation. Later Karl Pearson (1857-1936) discovered the mathematical formulation of correlation.
Alfred Binet (1851-1911) with student Théodore Simon developed in 1905 the Binet-Simon Scale of intelligence. Initially the test was used to study retardation in French schools. Later extended to normal children and adults. Binet believed that intelligence was composed of many factors and that it could be developed or ``taught''.
Clinical psychology in 1st half of 20th C used personality and aptitude assessment.