Psychology Of Individual Differences: What It Is And What It Studies

Psychology of individual differences

The psychology of individual differences studies how people have different ways of behaving and what causes this to be the case.

Its origins date back to classical times, although its constitution as a scientific branch of psychology occurred almost at the same time when psychology itself was established as a science, drawing heavily on evolutionary notions.

Next We will address in depth the psychology of individual differences a fundamental topic in all psychology faculties and in behavioral science research departments, and which allows us to understand that no two people are the same, their way of being a mixture of genes and environmental factors.

What is the psychology of individual differences?

The psychology of individual differences is the discipline that is responsible for studying why people are different from one another People are equal as long as we belong to the same species, however, it is also indisputable that no two people are the same, not even those who are identical twin brothers. Each person has characteristics that differentiate them from the rest, making them unique and unrepeatable individuals.

Individual differences are those differences that give each of us individuality. They distinguish us and differentiate us from the rest in various behavioral aspects, such as temperament, level of intelligence, propensity to suffer mental disorders and other aspects associated with the unique personality of the individual, all of them and their differences are the subject of study of differential psychology, which, in fact, is part of personality psychology.

In essence, we can say that the psychology of individual differences aims to describe, predict and explain interindividual variability (between people), intergroup (between groups) and intraindividual variability (of the same person throughout their life) in psychological areas. relevant, also focusing on the origin, manifestation and functioning of such variability.

Relationship with general psychology

The psychology of individual differences is often contrasted with general psychology, whose object of study is rather antagonistic. It is not that differential and general psychology are at odds in theoretical terms, in fact, their fields of study and knowledge complement each other, giving us greater knowledge about human behavior. General psychology is responsible for studying what all human beings have in common, what psychological aspects define us as a species as a whole.

General psychology uses an experimental method based on the ER (stimulus-response) or EOR (stimulus-organism-response) paradigm. Instead, The psychology of individual differences mainly uses the correlational method, based on the OER paradigm (organism-stimulus-response or individual-stimulus-behavior), which was postulated by Louis Leon Thurstone in 1923 taking a scientific approach centered on the person, whom he takes as a starting point and relegates the stimulus as a simple momentary circumstance of the around.

Although the OER paradigm is currently the most accepted within differential psychology, it has often been the subject of debate by several researchers in this field. Among them we can find the Spanish psychologist Antonio Caparrós, who proposed the RR paradigm, focused on the individual’s responses, their measurement and the relationships between them.

History of this psychological branch

The history of the psychology of individual differences can be divided into two major periods: pre-scientific period or historical background and scientific period or modern era. This last period would come along with the founding of psychology as an empirical science based on the scientific method, strictly speaking an event that occurred during the 19th century.

Pre-scientific period

Before the founding of psychology as a science and, in its extension, differential psychology, there was a series of knowledge, beliefs and ideas about why people behave in one way or another, whether in a “normal” or “normal” way. pathologically. Throughout all of History, human beings have asked ourselves What makes a person kind or unfriendly, more or less intelligent, functional or alienated?

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Although it is certain that the first human beings had to ask themselves why the members of their tribe were different from each other and from another tribe as well, the first written records on individual differences in the West are found in Classical Greece. We have an example of this in the figure of Plato, who tried to elucidate and explain why people behave differently, exposing it in his work “The Republic”, where these human differences are explicitly recognized.

In the Middle Ages the topic was also approached from a philosophical perspective. In fact, the scholastic theory taught in the faculties of the time addressed this question. Also It is during the Middle Ages that the Spanish doctor Juan Huarte de San Juan wrote his work “Examen de los Ingenios para las Ciencias” a text in which he talked about intelligence, differences in creativity between people and differences in certain abilities depending on sex.

The work of Juan Huarte de San Juan has been so important for psychology and, especially, the psychology of individual differences that this great thinker has ended up becoming the patron saint of all the faculties of Psychology in Spain, with the 23rd being a public holiday. February in his honor. He really is a pseudopatron, since he is not canonized by the Catholic Church and, ironically, his work was censored by the court of the Holy Inquisition.

Centuries later and well into the Renaissance and Enlightenment, other great thinkers would talk about individual differences in the Modern Age. Between the 18th and 19th centuries We can find philosophers such as Jean-Jacques Rousseau, Johann Heinrich Pestalozzi, Johann Friedrich Herbart and Friedrich Fröbel

The most modern figure who influenced and helped considerably in the founding of differential psychology as a scientific discipline is the naturalist Charles Darwin, promoter of several advances in biological science. Darwin’s studies, which would help him formulate his well-known theory of evolution, gave special emphasis to the individual differences found in individuals of various species and, also, in human beings, whom he had no qualms about considering animals and put them into his evolutionary theory.

Scientific era

Although several psychologists have been credited with creating the expression “individual differences,” one of them being William Stern, several historical records demonstrate that Charles Darwin already used them even in his best-known work “On the Origin of Species.” (1859), in addition to being one of the first to show scientific interest in the study of individual differences. This interest would be shared by his half-cousin Francis Galton in his attempt to quantify individual differences between people, and this is why some consider Galton the founder of differential psychology.

Galton was the first to try to apply the evolutionary principles of variation, selection and adaptation to the study of human beings. He did this by experimentally measuring individual differences in his Anthropometric Laboratory. In his attempt to organize the data he was collecting he introduced the statistical method with elements such as correlation, normal distribution and regression, concepts that would later be perfected by Karl Pearson and Irving Fisher.

General psychology gave rise to many other disciplines, including experimental psychology, interested in formulating general laws that explain human behavior in general. At first, psychology ignored individual differences and these were considered simple random errors. Later, J. McKeen Cattell, an experimental psychologist interested in interindividual and intergroup differences, would publish the first works that ended up redirecting the initial center of interest to such differences, progressively separating differential psychology from experimental psychology.

Throughout the 20th century, the psychology of individual differences would take on several impulses, including the creation and improvement of mental tests, tools that allowed various human characteristics to be apparently objectively measured. The first focused on intelligence and personality, having the Cattell personality test and the Binet-Simon intelligence scale. Psychometrics would take shape, helping in the maturation of psychological questionnaires thanks to the improvement of reliability and validity techniques.

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All these milestones would definitively make differential psychology independent, this being officially recognized in 1957 at the 65th Annual Convention of the American Psychological Association, whose director Lee Cronbach distinguished the scientific status of psychology from individual differences within the branches of modern psychology.

Between the 1950s and 1970s there was a great diversification in the investigations of individual differences Differential psychology was losing homogeneity and began to receive numerous criticisms from Clinical and Experimental Psychology. Starting in 1970, there would be a boom in this discipline, with the great impact of the so-called “cognitive revolution.”

Its objective

Like any other branch of psychology, individual differences aims to study human behavior. Nevertheless, Its more specific objective is to describe and explain interindividual, intraindividual and intergroup differences Furthermore, it aims to carry out a functional study of behavioral variability using a specific methodological approach.

Its main object of study focuses on interindividual differences, which refer to the fact that at a certain moment or situation different individuals behave differently. In order to best describe this variability, it is necessary to measure individual differences through psychometrics and tests of personality, intelligence and mental disorders.

Another object of study, not as studied but no less important, are intra-individual differences. That is, it is the study of the different ways of behaving of the same individual, comparing it with itself over time and in reference to a specific variable.

Regarding intergroup differences We refer to when the same psychological characteristic is observed or measured in different individuals Some of them tend to give similar answers or obtain scores on similar tests. Despite all this, group behavior in itself does not exist, but rather it is a generalization according to which the mean of a certain variable of the group members differs from that of other groups.


The method most used by differential psychology is correlational, which compares individuals and groups and is among the “ex post facto” methodologies, that is, the phenomenon is observed after it has occurred In most cases the independent variable is not manipulated, since its manipulation has already taken place naturally before and there is no way to manipulate it. The orientation of the psychology of individual differences is nomothetic, since it studies the characteristics shared between individuals that make up a homogeneous group.

Along with this method, cross-sectional correlation is added, in which representative samples of different populations are compared and is used to observe intergroup differences; and longitudinal correlational, which is based on carrying out successive measurements of the same subjects during an indefinite period of time, used to observe intra-individual differences.

Although it is common to use correlational methods, observational and experimental techniques can also be used, as is the retrospective method, although it does not have much relevance in differential psychology. This methodology is based on the collection of information using information extracted from the explanations made by the subjects themselves about their behavior, or using biographical data obtained from other sources, such as the testimony of loved ones.

Regarding the tools used in this discipline, we find a wide variety. We can find neurophysiological measures including electroencephalography (EEG), magnetic resonance imaging (MRI), positron emission tomography (PET)… These methods can be used to search for biomarkers of biologically based behavioral patterns (temperamental traits and symptoms of psychiatric disorders).

Other methods include behavioral experiments to observe how differently people behave when doing the same task. Behavioral experiments are often used in both personality and social psychology and lexical and self-report methods are included in which people are asked to complete questionnaires prepared by psychologists.

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Aspects studied

Among the most researched phenomena in psychology differences is intelligence, studied primarily in terms of performance and ability to perform tasks in academics, work, and everyday life. Its stability over time is also studied, whether it increases or decreases as one grows, what factors increase it (Flynn effect), differences between sexes and heritability and environmental influence. Additionally, the extremes are addressed, i.e. intellectual disability and giftedness.

Although not without controversy, the psychology of individual differences has also addressed the definition of intelligence Some understand it as something more or less homogeneous, while others speak of multiple intelligences. What is agreed upon is the unit used to measure this construct, speaking of intellectual quotient and accepting its distribution following the normal curve in the population.

Another aspect studied in differential psychology are moods and, above all, personality traits. To understand personality it is very important to consider variations in temperament, which constitutes the basic core of an individual. Currently it is possible to study the structure of this phenomenon thanks to lexical-factorial and biological-factorial models. Another concept closely related to personality is character, understood as the individual’s motivational disposition.

The debate in this psychological branch about the origin of individual differences is now classic. Although attempts have been made to use a scientific explanation for this, originally there were two extremist positions, one defending that everything was due to genetics, and that therefore human differences were hereditary; and another who argued that everything was due to the environment, with the differences being influenced by the environment. This debate has been called “nature vs. nurture”, that is, “nature vs. breeding”.

With the passage of time, an agreement was reached and today it is accepted that our way of being, our personality, intelligence and the appearance of mental disorders is due to both factors. It is indisputable that there must be some genetic load that explains our personality, but the environment must also exert some influence, especially if we take into account the countless experiments with monozygotic (identical) twins who, when raised separately, have behaviors in common. and some different behaviors.

Thus, the main debate in the psychology of individual differences has been resolved by establishing that there is an interaction between the person’s genotype and their environment, which gives rise to a particular phenotype, that is, the traits that end up manifesting in the person In fact, as a result of this internal debate in the psychology of differences, it has given rise to the constitution of disciplines that exclusively study the weight of the environment and heredity in the way people are, as is the case of Genetics. Quantitative.

Applications of this branch

The psychology of individual differences It has a lot of application in the field of industrial and organizational psychology, which specializes in human behavior in the workplace. Organizational psychologists often consult with companies and look for ways to improve productivity and morale. These investigate aspects such as the differences between workers who are happy and productive and those who are not so happy and seem unmotivated with their jobs.

Some individual differences psychologists study human behavior based on biological differences. This type of research explores aspects such as heritability, physical traits and reactions to drugs Biological differences between individuals may be the key to understanding why people behave and respond differently when taking the same medication, allowing us to select drugs that are more effective depending on which patients have a specific genotype.