Differential Psychology

Differential psychology is an area of psychology in which individual differences in behavior are studied along with the processes that underlie the differences.

The study of individual differences includes evaluating how people feel, what they want and need, and what they do. It involves evaluating differences in such factors as an individual's affect, behavior, cognition, and motivation. These factors are influenced both by biological causes as well as environmental events and essentially involves all areas of psychology (e.g., cognitive, social, neuro-and behavioral psychology, and more). Differences in physical abilities may also be involved, including taste, smell, and strength.


Bell curve—
In mathematics and data analysis, a graph depicting expected or typical distribution of specific variables, featuring a large rounded peak or bell that slopes downward on each side of the peak. The majority or most probable factors cluster at the center and highest point of the curve, and distribution decreases toward the ends of the curve.
Factor analysis—
In research, expression of the values of observed data as functions of a number of possible causes to help determine which are the most significant.
Normal probability distribution—
In probability theory, normal distribution in the most common continuous probability distribution of a specific subject, factor, or event.
Principal component analysis—
In statistics, a procedure that uses statistically independent transformation to convert a set of observations of variables into a set of values of uncorrelated variable called principal components.

Individual differences are considered important because they allow psychologists to explain differences in behavior. Differences are found in personality, levels of intelligence, cognitive development, memory, and physical factors such as height, weight, gender, and age. Differential psychologists study these variables in conjunction with the motivation, values, perceptions, and self-esteem of individuals. Specific variables between two different groups of individuals (e.g., men and women) may be compared, looking at how they are distributed within the given populations. Most differences can be measured on a continuum that follows the normal probability distribution as displayed on a bell curve. The majority of subjects or factors or events will be clustered at the peak of the curve (the bell) and extremes will fall to the sides of the curve. This type of factor analysis research requires statistical controls so that no biases are introduced into the evaluation. For example, observations about group differences can sometimes be turned into stereotypes when mean characteristics are indiscriminately ascribed to all individuals in a group and when differences between groups are viewed as unchangeable and only determined genetically.

In addition to the use of data reduction methods such as factor analysis and principal component analysis, research methods in differential psychology range from laboratory experiments to longitudinal studies in different geographical regions. Psychological testing is used extensively in differential psychology to measure differences in cognitive ability and intelligence. Advances in testing methods and the development of projective tests to determine interests, attitudes, and emotional responses have helped to advance the discipline of differential psychology, allowing both quantitative and qualitative analysis of individual psychological characteristics to be determined.

Research on individual differences may include identifying how differences in one situation may predict differences in other situations and also testing theories about the dynamics of individual differences. One of the biggest questions to be answered in the study of individual differences is whether biological or sociocultural factors are responsible for specific characteristics of individuals. Mathematical and experimental approaches and methods are developed to help clarify the influence of age and sex differences as well as the influence of personal values and environmental factors. Ongoing research in personality psychology includes investigation of cognitive abilities, interpersonal styles, and emotional reactivity; the analysis of genetic codes; and the study of social, ethnic, and cultural differences. Correlations between psychological characteristics and physiological characteristics are often the basis of studies exploring not only intellectual variables but differences in creative and organizational abilities of individuals. Practical applications of data from differential psychology studies may include tasks such as the selection and training of personnel and the diagnosis and prediction of the development of individuals’ unique characteristics, tendencies, and abilities.



Cerone, Daniel, and Lawrence A. Pervin. Personality: Theory and Research, 12th ed. Hoboken, NJ: Wiley & Sons, 2013.

Ourth, Lynn, and Stephanie Metzler, eds. Differential Psychology: A Study of Individual Differences. Dubuque, IA: Kendall Hunt, 2002.


Kanai, R., and G. Rees. “The Structural Basis of InterIndividual Differences in Human Behaviour and Cognition.” Neuroscience 12 (June 2011): 231–41.

Revelle, W., J. Wilt, and D. M. Condon. “Individual differences and differential psychology.” Northwestern University Handbook of Individual Differences: The Personality Project (May 2010): 1–17.