Psychology of individual differences: what it is and what it studies

The psychology of individual differences studies how people behave in different ways and what causes them.

Its origins date back to classical times, although its constitution as a scientific branch of psychology occurs almost simultaneously when psychology itself was incorporated as a science, feeding heavily on evolutionary notions.

Then we will discuss in depth the psychology of individual differences, A fundamental stake in all the faculties of psychology and in the research departments of behavioral sciences, and which makes it possible to understand that no two people are alike, being 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 of studying why people are different from each other. People are equal as long as we are of the same species, however, it is also indisputable that no two people are equal, not even those who are identical twin brothers. Each person has characteristics that differentiate them from others, making them unique and irreplaceable individuals.

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

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

    Relationship with general psychology

    Often the psychology of individual differences is opposed to general psychology, The object of the study is rather antagonistic. It is not that differential and general psychology is hostility in theoretical terms, in fact, their fields of study and knowledge complement each other in granting love a knowledge of human behavior. General psychology is concerned with the study of what all of us 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. However, the psychology of individual differences mainly uses the correlational method, based on the paradigm of OER (Organism-stimulus-response or individual-stimulus-behavior), which was postulated by Louis Leon Thurstone in 1923 by adopting a scientific person-centered approach, which he takes as a starting point and relegates the stimulus as a mere circumstance momentary environment.

    Although the OER paradigm is currently the most accepted in 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 responses of the individual, his size and the relationships between them.

      History of this psychological branch

      The history of the psychology of individual differences can be divided into two broad periods: pre-scientific period or historical context and scientific period or modern era. This last period would coincide with the foundation of psychology as an empirical science and based on the scientific method itself., Event given in the 19th century.

      pre-scientific period

      Before the founding of psychology as a science and, to its extent, of differential psychology, there was a number of knowledge, beliefs, and ideas about why people behave in one way or another. on the other hand, already in a “normal” way. . Throughout the history of human beings we have asked ourselves what makes a person nice or hostile, more or less intelligent, functional or alienated.

      While it is certain that early humans must have wondered why members of their tribe were different from each other and from another tribe as well, the earliest written history of individual differences in the West can be found in Greece. We have an example of this in the figure of Plato, who tried to elucidate and explain why people behave differently, by exposing it in his work “The Republic”, where these human differences are explicitly recognized.

      In the Middle Ages, the subject was also approached from a philosophical perspective. In fact, the scholastic theory taught in the faculties of the time answered this question. too much it was in the Middle Ages that the Spanish physician Juan Huarte de San Juan wrote his book “Examining gadgets for science”, Text in which he talks about intelligence, differences in creativity between people and differences in certain skills based on gender.

      The work of Juan Huarte de San Juan was so important for psychology and, in particular, the psychology of individual differences that this great thinker ended up becoming the owner of all the faculties of psychology in Spain, on vacation on February 23 in his honour. He is truly a pseudo-patron, as he is not canonized by the Catholic Church and, ironically, his work has been censored by the court of the Holy Inquisition.

      Centuries later and already well into the Renaissance and the Enlightenment, other great thinkers were speaking of individual differences in the modern age. Between the 18th and 19th centuries one can meet philosophers such as Jean-Jacques Rousseau, Johann Heinrich Pestalozzi, Johann Friedrich Herbart and Friedrich Fröbel.

      The most modern figure who has greatly influenced and contributed to the founding of differential psychology as a scientific discipline is the naturalist Charles Darwin, the driving force behind the various advances in biological science. Darwin’s studies, which would serve to formulate his well-known theory of evolution, placed particular emphasis on the individual differences found in individuals of various species and also in humans, who had no problem considering animals. and place them in their evolutionary theory.

      Scientific period

      Although several psychologists have been credited with coining the term “individual differences”, one of them being William Stern, several historical documents show that Charles Darwin and used them even in his best-known work “On the Origin of Species” (1859), besides being one of the first to show a scientific interest in the study of individual differences. This interest is said to be shared by his half-cousin Francis Galton in his attempt to quantify the individual differences between people, which is why some consider Galton to be 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 anthropometry lab. In his attempt to organize the data he collected, 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.

      From general psychology will give birth to many other disciplines, including experimental psychology, interested in formulating general laws which explain human behavior in general. At first, psychology ignored individual differences and these were considered like simple random errors. Later, J. McKeen Cattell, an experimental psychologist interested in interindividual and intergroup differences, will publish the first papers which ultimately redirected the initial attention to these differences, gradually separating differential psychology from experimental psychology.

      Throughout the twentieth century, the psychology of individual differences would take on several impulses, among which creating and improving mental tests, Tools that apparently objectively measured various human characteristics. The first focused on intelligence and personality, passing the Cattell Personality Test and the Binet-Simon Intelligence Scale. Psychometrics would take shape, helping the maturation of psychological questionnaires through improved techniques of reliability and validity.

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

      Between the 1950s and 1970s there was great diversification in surveys of individual differences. Differential psychology was losing its homogeneity and began to receive much criticism from clinical and experimental psychology. From 1970, there would be a boom in this discipline, with the great impact of the so-called “cognitive revolution”.

        Your goal

        Like any other branch of psychology, that of individual differences aims to study human behavior. However, its more specific objective is to describe and explain interindividual, intraindividual and intergroup differences. In addition, it aims to conduct a functional study of behavioral variability through a specific methodological approach.

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

        Another object of study, not as studied but no less important, is the intra-individual differences. That is to say, it is the study of the different ways of behaving of the same individual, by comparing himself to himself over time and with reference to a given 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 answers or get scores on similar tests. Despite all this, group behavior by itself does not exist, but is a generalization that the mean of a given variable of group members differs from other groups.


        The most widely used method in differential psychology is correlation, which compares individuals and groups and is part of “ex post facto” methodologies, i.e. the phenomenon is observed after it has occurred. In most cases, the independent variable is not manipulated, because its manipulation has happened 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 the individuals who make up a homogeneous group.

        To this method is added cross-correlation, in which representative samples from different populations are compared and are used to observe intergroup differences; and longitudinal correlation, which is based on making successive measurements of the same subjects over an indefinite period of time, used to observe intra-individual differences.

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

        As for the tools used in this discipline, we find a great 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 behavioral models based on biology (temperament traits and symptoms of psychiatric disorders).

        Other methods include behavioral experiments to observe how different people behave when performing the same task. Behavioral experiments are often used in both personality psychology and social psychology, And includes lexical methods and self-assessments in which people are asked to complete questionnaires prepared by psychologists.

        aspects studied

        Among the most studied phenomena in the psychology of differences is intelligence, studied primarily in terms of performance and the ability to perform tasks in academia, work and everyday life. It also studies its stability over time, whether it increases or decreases as it grows, what factors increase it (Flynn effect), gender differences and heritability and environmental influence. In addition, extremes are discussed, that is to say 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 we agree on is the unit used to measure this construct, talking about IQ and accepting its distribution along the normal curve in the population.

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

        The debate in this psychological branch on the origin of individual differences is already classic. Although an attempt has been made to use a scientific explanation for this, there were originally two extremist positions, one asserting that it was all genetics, and therefore human differences were hereditary; and another who argued that it was all due to the environment, the differences being influenced by the environment. This debate has been called “nature versus food”That is to say “nature against parenthood”.

        Over time, an agreement was reached and today it is accepted that our way of being, our personality, our intelligence and the appearance of mental disorders are due to two factors. It is indisputable that a genetic load must have to explain our personality, but also the environment must exert a certain influence, especially if one takes into account the countless experiences with monozygotic (identical) twins during their breeding. separately have common behaviors 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 genotype of the person and his environment, which it gives rise to a particular phenotype, that is to say to the traits which end up being manifest 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 which exclusively study the weight of the environment and heritage in the way people are, as in the case of quantitative genetics.

        Applications of this branch

        The psychology of individual differences it has a lot of application in the field of industrial psychology and organizations, Which specializes in human behavior in the workplace. Organizational psychologists often consult with companies and look for ways to improve their productivity and morale. These study aspects such as the differences between happy and productive workers and those who are not and seem demotivated by their place. of work.

        Some individual difference psychologists study human behavior in terms of biological differences. This type of research explores aspects such as heritability, physical traits, and drug reactions. Biological differences between individuals may be the key to understanding why people behave and respond differently to taking the same drug, allowing them to select more effective drugs based on patients who have a particular genotype.

        Bibliographical references:

        • Eysenck, Michael W (1994). Individual differences: normal and abnormal. Hillsdale, NJ: L. Erlbaum Partners
        • Maltby, J .; Day, L. and Macaskill, A. (2007). Personality, individual differences and intelligence. London: Pearson Education.
        • Buss, DM and Greiling, H. (1999). Adaptive individual differences. Personality diary. 67 (2): 209-243. CiteSeerX doi: 10.1111 / 1467-6494.00053.
        • Chamorro-Premuzic, T. and Furnham, A. (2006). Intellectual competence and intelligent personality: a third way in differential psychology. General review of psychology. 10 (3): 251-267. doi: 10.1037 / 1089-2680.10.3.251. S2CID 146278640.

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