Observations about a persons quality of vocabulary, for example, would be put into the category of

personality assessment, the measurement of personal characteristics. Assessment is an end result of gathering information intended to advance psychological theory and research and to increase the probability that wise decisions will be made in applied settings (e.g., in selecting the most promising people from a group of job applicants). The approach taken by the specialist in personality assessment is based on the assumption that much of the observable variability in behaviour from one person to another results from differences in the extent to which individuals possess particular underlying personal characteristics (traits). The assessment specialist seeks to define these traits, to measure them objectively, and to relate them to socially significant aspects of behaviour.

A distinctive feature of the scientific approach to personality measurement is the effort, wherever possible, to describe human characteristics in quantitative terms. How much of a trait manifests itself in an individual? How many traits are present? Quantitative personality measurement is especially useful in comparing groups of people as well as individuals. Do groups of people from different cultural and economic backgrounds differ when considered in the light of their particular personality attributes or traits? How large are the group differences?

Overt behaviour is a reflection of interactions among a wide range of underlying factors, including the bodily state of the individual and the effects of that person’s past personal experiences. Hence, a narrowly focused approach is inadequate to do justice to the complex human behaviour that occurs under the constantly changing set of challenges, pleasures, demands, and stresses of everyday life. The sophisticated measurement of human personality inescapably depends on the use of a variety of concepts to provide trait definitions and entails the application of various methods of observation and evaluation. Personality theorists and researchers seek to define and to understand the diversity of human traits, the many ways people have of thinking and perceiving and learning and emoting. Such nonmaterial human dimensions, types, and attributes are constructs—in this case, inferences drawn from observed behaviour. Widely studied personality constructs include anxiety, hostility, emotionality, motivation, and introversion-extroversion. Anxiety, for example, is a concept, or construct, inferred in people from what they say, their facial expressions, and their body movements.

Personality is interactional in two senses. As indicated above, personal characteristics can be thought of as products of interactions among underlying psychological factors; for example, an individual may experience tension because he or she is both shy and desirous of social success. These products, in turn, interact with the types of situations people confront in their daily lives. A person who is anxious about being evaluated might show debilitated performance in evaluative situations (for example, taking tests), but function well in other situations in which an evaluative emphasis is not present. Personality makeup can be either an asset or a liability depending on the situation. For example, some people approach evaluative situations with fear and foreboding, while others seem to be motivated in a desirable direction by competitive pressures associated with performance.

Measuring constructs

Efforts to measure personality constructs stem from a variety of sources. Frequently they grow out of theories of personality; anxiety and repression (the forgetting of unpleasant experiences), for example, are among the central concepts of the theory of psychoanalysis. It is understandable that efforts would be made to quantify one’s degree of anxiety, for example, and to use the score thus obtained in the assessment of and in the prediction of future behaviour. Among the major issues in the study of personality measurement is the question of which of the many personality constructs that have been quantified are basic or fundamental and which can be expected to involve wasted effort in their measurement because they represent poorly defined combinations of more elemental constructs; which measurement techniques are most effective and convenient for the purpose of assessment; and whether it is better to interview people in measuring personality, or to ask them to say, for example, what an inkblot or a cloud in the sky reminds them of.

Efforts to measure any given personality construct can fail as a result of inadequacies in formulating or defining the trait to be measured and weaknesses in the assessment methods employed. An investigator might desire to specify quantitatively the degree to which individuals are submissive in social and competitive situations. His effectiveness will depend on the particular theory of submissiveness he brings to bear on the problem; on the actual procedures he selects or devises to measure submissiveness; and on the adequacy of the research he performs to demonstrate the usefulness of the measure. Each of these tasks must be considered carefully in evaluating efforts to measure personality attributes.

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The methods used in personality description and measurement fall into several categories that differ with regard to the type of information gathered and the methods by which it is obtained. While all should rely on data that come from direct observations of human behaviour if they are to have at least the semblance of scientific value, all may vary with regard to underlying assumptions, validity, and reliability (consistency, in this case).