Idiographic Methods

Introduction

Idiographic methods of psychological assessment are techniques designed to capture the unique and potentially idiosyncratic qualities of the individual. The assessor seeks to identify the constellation of psychological attributes that best characterizes the particular individual who is the target of assessment.

The idea of idiographic assessment can be contrasted with that of nomothetic assessment. Nomothetic methods (from the Greek for ‘law’, nomos, referring here to the search for universal scientific laws) characterize individuals via a fixed set of psychological variables and assessment procedures; that is, variables and procedures that do not change from one person to the next. In nomothetic assessment, a primary goal is to [Page 457]describe individuals in relation to the population at large; for example, people may be ranked on interindividual-difference dimensions. In contrast, idiographic methods (from the Greek idios, referring to personal, private, and distinct characteristics) employ psychological constructs and assessment procedures that may vary from one person to the next. The primary aim is to describe qualities of the individual and the within-person organization among these qualities. In idiographic assessment, describing the individual with fidelity is the paramount task, whereas characterizing the individual's standing with respect to the population at large is of secondary importance.

This entry discusses the rationale behind idiographic assessment and reviews specific idiographic techniques. The focus primarily is on assessment in personality and clinical psychology. Personality psychologists have devoted particular attention to idiographic methods, spurred by Allport's (1937) highlighting of the organized qualities of the unique individual. Clinical psychologists' need to understand individual clients in depth inherently motivates idiographic methods in this field; indeed, although this entry focuses on quantitative idiographic assessment techniques, one should note that clinical case studies also constitute idiographic methods.

Rationale for Idiographic Assessment

To the extent that qualities of human nature are universal, idiographic methods might seem unnecessary. In principle, assessing universal aspects of psychological variation might be sufficient to characterize individual persons. There are, however, three reasons for adopting idiographic methods.

One is simply that assessors may desire more detailed information than is provided by nomothetic techniques. Describing individuals within a universal system of individual differences is only a first step in capturing the features of individual persons, who possess unique qualities that may require more detailed, individual-focused assessment techniques to be fully revealed.

A second reason for adopting idiographic methods involves predictive utility. The assessor may wish to predict a particular behavioural outcome, yet may know that established nomothetic methods already have proven to have little predictive value in the domain under investigation. This might occur, for example, if individuals tend to display criterion behaviours only in highly specific contexts that vary idiosyncratically from one person to the next. In such cases, pragmatic considerations motivate the use of idiographic techniques.

A third reason is not merely pragmatic, but conceptual. Theoretical considerations may suggest that standard nomothetic assessments do not adequately represent the psychological qualities in which the assessor is interested. Nomothetic assessments typically describe people according to individual-difference dimensions, where those dimensions commonly are statistical factors identified in analyses of the population at large. The factors, then, are statistical properties of populations, not of individuals. On purely statistical grounds, one cannot assume that group-level statistical parameters necessarily will capture the qualities of each individual in the group. Person-centred rather than population-based methods thus may be required to capture psychological qualities at the level of the individual.

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