individual difference

Differential psychology is the branch of psychology that studies individual and group differences in behavior. It emphasizes that these differences are quantitative, meaning people vary along a continuous scale rather than falling into distinct types. Most psychological characteristics follow a bell-shaped normal distribution, with most individuals clustering around the average. These individual differences are observed not only in humans but also across the animal kingdom, affecting traits like learning and motivation.1

The study of intelligence, a key area within differential psychology, has been approached through psychometric theories. These theories aim to understand the structure of intelligence, often using tests to measure abilities. Early work by Charles Spearman suggested a general factor ('g') underlying all intellectual tasks, while others, like L.L. Thurstone, proposed multiple primary mental abilities. Modern theories often view intelligence hierarchically, acknowledging both general and specific abilities, and recognize the significant interplay between heredity and environment in shaping traits like intelligence.23