At the level of the type, Eysenck proposes three other broad dimensions: neuroticism, psychoticism, and intelligence. He is careful to point out that no one is ever a pure anything-a neurotic person's not neurotic all the time, for example, and quite clearly one cannot be intelligent and nothing else. Still, our typical levels of behavior do differ, so that each of us reflects a distinctive combination of these four dimensions and their many sub dimensions. Thus the in , if it were to represent the person described properly, would have to be greatly expanded so as to include each type that contributes to this individual's personality, together with each type's subsidiary traits and habitual specific responses.
J.P. Guilford, a pioneer in the technique of factor analysis, has also represented personality traits or dimensions in a hierarchical fashion.
How did Eysenck derive his types, or dimensions, according to which people vary? He began, during World War II, by studying some of the many soldiers who were treated at the hospital where he served as staff psychologist. Eysenck's (1947) first major work studied some 700 military psychiatric cases, and it led to the isolation of the two variables of introversion-extraversion and normality-neuroticism. These two factors were extracted from the analysis of a large number of variables, many of which were traits (e.g., anxiety, dependency) but some of which were factual data (e.g., age, martial status). Much of Eysenck's initial database consisted of ratings by psychiatrists and life-history information. Subsequent explorations, however, employed other kinds of data sources such as questionnaires and performance tasks
