While prominent psychologists, including Stern, have been widely credited for the concept of differential psychology, historical records show that it was Charles Darwin (1859) who first spurred the scientific interest in the study of individual differences.
In this context, differences between individuals in their reaction to the experimental and control manipulations are actually treated as errors rather than as interesting phenomena to study.
[citation needed] Individual differences research typically includes personality, temperament (neuro-chemically based behavioural traits), motivation, intelligence, ability, IQ, interests, values, self-concept, self-efficacy, and self-esteem (to name just a few).
These methods can be used for a search of biomarkers of consistent, biologically based behavioural patterns (temperament traits and symptoms of psychiatric disorders).
Behavioural experiments are often used in personality and social psychology, and include lexical and self-report methods where people are asked to complete paper-based and computer-based forms prepared by psychologists.