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The Idiographic vs. the Nomothetic debate


Nomothetic Approach
Idiographic Approach
Definitions
The approach of investigating groups of people to try and find general laws of behaviour that apply to everyone.
The approach of investigating individuals in personal,in depth details to achieve a unique understanding of them.
Assumptions and Methods
The nomothetic approach, from the Greek word 'nomos' meaning 'law', assumes that since individuals are merely complex combinations of many universal laws, people are best studies by large scale preferentially experimental, methods to identify those laws.
Differences between people are only quantitative so an individual will be compared to others, classified with others, measured as a score upon a dimension, or be a statistic supporting a general principle.
The idiographic approach, from the Greek word 'idios' meaning private or personal, assumes that since each human is unique, they are best studied by the case study method to provide a detailed understanding of the individual.
Differences between people are qualitative so study should focus on the unique aspects of, and variability within, a person's thinking and behaviour.  By studying these personal variables, norms or trends, predictions can be made, but only about that particular individual.
Examples from Psychology
Nomothetic research is the main approach taken in scientifically orientated psychology.  The Behaviourist  experiments in learning were conducted on many participants (mostly rats and pigeons), replicated until the general laws of learning were well established, then even generalised as universal laws of nature to humans.  The social psychology experiments of Asch and Milgram used the nomothetic approach to reach conclusions about people in general by comparing groups of participants.  All psychological theories that propose generalised principles of behaviour have nomothetic assumptions - Eysenck's personality theory places individuals along a universal dimension of extroversion/introversion, intelligence test measure people along a scale of I.Q. scores, and classification manuals for mental disorder e.g. I.C.D (11) and D.S.M.-5-TR, classify people as suffering from particular types of disorder.
The Idiographic approach is taken, in its pure form, more rarely in psychology that the nomothetic approach.  Humanistic psychologist focus on the unique characteristics and life experiences of individuals.  Some, such as Tomas Szasz (1972), have rejected the grouping of individuals into general diagnostic categories like 'schizophrenia' preferring to focus on their unique 'problems with living'.
In personality research, Allport (1961) made the distinction between common and individual traits, while Kelly (1955) tried to identify the way individual perceive the world in terms of personal constructs.
Freud (1909) used the clinical case study method and aimed to identify the unique life experiences in a patient's history that led to their psychological problems.  Nevertheless, he did argue that there were similar processes and mental structures present in everyone that created certain types of problem.
Evaluation
The nomothetic approach is in tune with the deterministic, law-abiding nature of science, and has been applied very successfully in other sciences as well as psychology.  The ability to generalise laws and compare groups of people is very useful in predicting and controlling behaviour in general.  For example, personality questionnaires and mental disorder classification manuals have been used in the selection of personnel and the diagnosis and treatment of disorders.  The drawback, however, is that this approach leaves us with a more superficial understanding of any one person - you and I may have the same I.Q., but I may have answered different questions to you.  Also a piece of nomothetic research may tell me I have a 1% chance of becoming schizophrenic, but it will not tell me if I am in that 1%.
The idiographic approach provides a more complete and global understanding of the individual.  In some counselling and psychotherapy the goal is greater self understanding.  Nomothetic generalisation may be too vague or inaccurate for the individual.  An idiographic approach may help to balance the neglect of uniqueness in psychology - a science dominated by experiments that actively try to control and eliminate individual differences (participant variables).
Replication and prediction for an individual is possible in an idiographic approach but we cannot legitimately generalise (apply) the findings to other people, which limits its usefullness and application in psychology.
The idea that people are so unique they cannot be compared in any way seems contradicted by psychological research.
Evaluation
Clearly, bot approaches seem necessary for a complete study of psychology - if the aims of science are to describe, understand, predict, and control, then idiographic methods may be more suitable for the first two aims and the nomothetic methods for the latter two.  As Kluckholm and Murray (1953) comment, every person is in some respects 1) like no other person, 2) like some other people and 3) like all other people.  If there were no common points between individuals then nobody would be able to understand each other!
In the case of abnormality, nomothetic classification allows research to be carried out on groups of people suffering similar symptoms in the hope that a similar cause and cure can be identified, while an idiographic approach may be useful to deal with the particular and perhaps unique set of problems encountered by each patient.


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