Nomothetic psychology searches for general laws that apply across groups of people, using quantitative, statistical methods. Idiographic psychology instead studies one individual in rich, qualitative depth, to understand what makes that person unique.
Nomothetic Approach
The nomothetic approach in psychology focuses on general principles and laws that apply to groups of individuals.
It seeks to identify universal patterns, traits, and characteristics that generalize across people. Researchers use quantitative methods and statistical analysis to draw conclusions about human behavior.
The term “nomothetic” comes from the Greek word “nomos,” meaning “law.”
Psychologists who adopt this approach are mainly concerned with studying what we share with others (i.e., similarities between people).
Therefore, the nomothetic approach involves establishing laws or generalizations that apply to everyone.
Nomothetic laws take three main forms:
- Classifying people into groups (such as the DSM-V for classifying people with mood disorders);
- Establishing principles (such as the behaviorist laws of learning); and
- Establishing dimensions (such as Eysenck’s personality inventory, which allows for comparisons between people).
Researchers typically obtain these laws through experiments and observations that produce quantitative data. Researchers then analyze group averages statistically to predict how people in general will behave.
Personality: – A Nomothetic Approach
The psychometric approach to the study of personality compares individuals in terms of traits or dimensions common to everyone. This is a nomothetic approach, and two examples are Hans Eysenck’s type and Raymond Cattell’s 16PF trait theories.
Eysenck and Cattell both assumed that a small number of traits capture the basic structure of every personality. Individual differences, on their view, can be measured along these shared dimensions.
A broad consensus has since emerged around five core traits, often called the Big Five: extroversion, agreeableness, conscientiousness, emotional stability, and openness to experience.
From a nomothetic point of view, these are considered to describe the psychologically significant aspects of any personality adequately.
Strengths
- Scientific Rigor: Precise measurement, controlled methods, and large-group studies allow replication and generalization.
- Built Psychology’s Evidence Base: Testable laws and theories developed this way helped psychology become a science.
- Efficient Data Collection: Once a questionnaire or experiment is designed, researchers can collect data from large samples quickly.
Limitations
- Group-to-Individual Gap: Predictions made about groups may not apply to any one individual.
- Loses the Whole Person: Critics argue the approach reduces people to scores on a few dimensions.
Idiographic Approach
The idiographic approach in psychology focuses on understanding individuals in their unique context.
It aims to uncover the specific, individualized factors behind a person’s behavior and psychological functioning. Researchers use qualitative methods and in-depth analysis to gain rich insight into that one individual’s life.
The term “idiographic” comes from the Greek word “idios,” meaning “one’s own” or “particular.” Psychologists interested in this aspect of experience want to discover what makes each of us unique.
No general laws are possible because of chance, free will and the uniqueness of individuals.
Methods of research include case studies, unstructured interviews, self-reports, autobiographies, and personal documents.
Personality: – An Idiographic Approach
At the other extreme, Gordon Allport and Henry Odbert combed an unabridged dictionary and catalogued over 18,000 separate terms describing personal characteristics (Allport & Odbert, 1936).
Some of these are common traits, which could be investigated nomothetically. But Allport argued the majority are unique dispositions, built from each person’s own life experiences.
He argues that they cannot be effectively studied using standardized tests. What is needed is a way of investigating them idiographically.
Carl Rogers, a Humanist psychologist, adapted a technique originally devised by William Stephenson to do this: the “Q-sort.” Rogers used it to measure a person’s self-concept against their ideal self across therapy. First, the subject is given a large set of cards with a self-evaluative statement written on each one.
For example, “I am friendly” or “I am ambitious,” etc. The subject is then asked to sort the cards into piles. One pile contains statements that are “most like me,” one pile contains statements that are “least like me,” and one or more piles hold statements that are in-between.
In a Q-sort, the number of cards, piles, and type of question can all be varied (e.g., How am I now? How was I in the past? How does my partner see me? How would I like to be?). This gives a potentially infinite number of variations. That fits an idiographic view perfectly: there are, in principle, as many different personalities as there are people.
Personality theorist George Kelly pushed the idiographic argument even further than Allport. His personal construct theory treats each person as a lay scientist. On this view, we all build and test our own private system of constructs, such as “kind versus cruel,” to predict events (Kelly, 1955).
Kelly’s chief technique is the repertory grid. It asks someone to name key figures in their life, then rate every figure on personal constructs the respondent generates themselves. Because each construct comes fresh from that one respondent, two people’s grids need not share a single construct.
Strengths
- Focus on the Individual: Gordon Allport argued that only by knowing someone as a person can we predict what they will do in a given situation.
- Generates New Hypotheses: Rich, individual findings often suggest ideas that later nomothetic research can test.
Limitations
The idiographic approach is time-consuming and costly: studying individuals in this depth demands considerable resources.
Critical Evaluation
The Case for Treating Them as Rivals
The two traditions chase different goals. Nomothetic research wants a general law; idiographic research wants to understand one case in depth.
Historically, nomothetic, quantitative work has been treated as the more scientific, publishable strand of psychology. Idiographic, case-based work has often been dismissed as merely anecdotal.
The Case for Treating Them as Complementary
Even Gordon Allport, the leading voice for idiographic description, argued that common, nomothetic traits still have real, if limited, value for rough comparison (Allport, 1961). He wanted both levels of description working together, not one replacing the other.
The repertory grid makes the same point directly: used freely, it captures one person’s own constructs. Standardised in advance, that same tool becomes a nomothetic measure for comparing whole groups. Idiographic and nomothetic, in other words, describe how a method is used, not two fixed kinds of method.
Modern methods blur the old lines further. Repeated within-person measurement, sometimes called an “N-of-1” design, tracks one person many times over. It can be modelled with the same statistical rigor once reserved for large, between-person studies (Piccirillo & Rodebaugh, 2019).
Contemporary Research
A widely discussed 2018 study tested this question directly, using real data instead of theoretical argument.
Aim: Fisher, Medaglia, and Jeronimus (2018) wanted to know how far a correlation calculated across a group actually reflects the pattern inside any one member of that group.
Method: The researchers drew on studies where people had reported their own moods and anxiety repeatedly, often daily, over several weeks. They then compared the correlation between two variables two ways: once across all participants, and once within each single participant’s own repeated reports.
Results: Correlations calculated within one person varied enormously, roughly four times more than correlations calculated across the whole group. Many individuals showed a pattern much weaker, much stronger, or even reversed compared with the group-level result.
Conclusion: This is a serious threat to any research, treatment, or advice that assumes a group-level finding applies to one specific person. Psychology needs to build far more within-person research into its evidence base, not treat it as a mere add-on (Fisher, Medaglia, & Jeronimus, 2018).
This finding gives Allport’s old argument a precise, modern number: averaging across people really can hide what is true of any one of them.
Conclusion
Idiographic and nomothetic approaches should not be seen as conflicting. It is more helpful to see them as complementary.
The insights from an idiographic approach can shed more light on the general principles developed using the nomothetic approach.
For example, Bowlby’s theory of maternal deprivation suggests that extreme maternal deprivation is irreversible. This theory was developed using a nomothetic approach.
However, the case of Koluchova’s twins demonstrates that in this single, idiographic case, maternal deprivation was overcome. Bowlby’s theory can, therefore, be challenged.
As always, it is best to take a combined approach. Millon and Davis (1996) suggest research should start with a nomothetic approach, then move to a more idiographic approach once general laws are established. This combined approach captures the strengths of both traditions.
Key Takeaways
- Two Aims: Nomothetic research seeks general laws across groups; idiographic research seeks deep understanding of one individual.
- Different Outputs: Nomothetic work produces group averages, classifications, and dimensions. Idiographic work produces a rich account of one case.
- Allport’s Argument: Gordon Allport argued personality science needs common traits for rough comparison and individual traits for truly knowing a person.
- Repertory Grid: Kelly’s technique can be used idiographically or nomothetically, showing the split describes how a method is used, not a fixed type of method.
- Group-to-Individual Gap: A 2018 study found within-person patterns often differ sharply from group-level correlations (Fisher et al., 2018).
- Best Used Together: Most psychologists now treat the two approaches as complementary: nomothetic findings structure understanding, and idiographic depth tests and refines it.
References
Allport, G. W. (1961). Pattern and growth in personality. Holt, Rinehart & Winston.
Allport, G. W., & Odbert, H. S. (1936). Trait-names: A psycho-lexical study. Psychological Monographs, 47(1), i–171. https://doi.org/10.1037/h0093360
Fisher, A. J., Medaglia, J. D., & Jeronimus, B. F. (2018). Lack of group-to-individual generalizability is a threat to human subjects research. Proceedings of the National Academy of Sciences, 115(27). https://doi.org/10.1073/pnas.1711978115
Kelly, G. A. (1955). The psychology of personal constructs. Norton.
Piccirillo, M. L., & Rodebaugh, T. L. (2019). Foundations of idiographic methods in psychology and applications for psychotherapy. Clinical Psychology Review, 71, 90–100. https://doi.org/10.1016/j.cpr.2019.01.002
