“A New Measure of Introversion-Extroversion”, 1941 (; backlinks; similar):
This paper describes the development of relatively independent measures for 3 types of Introversion-Extroversion: Thinking. Social, and Emotional. The need for clarifying the concept of I-E and for devising new inventories can best be understood by reviewing the confusion concerning its nature and measurement. In the effort to simplify the original complex description of I-E by Jung, psychologists either have introduced new concepts or emphasized varying phases of Jung’s definition. In this process of elaboration, they have actually complicated rather than clarified the idea of I-E. The use of these terms in the popular literature has only added to the confusion. Unfortunately, introversion, at least in the popular writings on psychology, has come to denote an undesirable personality tendency which borders on a neurotic condition.
In general, the available I-E inventories purport to measure a general, undifferentiated trait. However, the intercorrelations between the published inventories are surprisingly low. Only 5 of the 19 coefficients of intercorrelation reported in the literature for nine inventories are above 0.40, and only 2 are above 0.80. The 2 coefficients above 0.80 are between 2 inventories and revised forms of these same inventories.
…This study has reduced the confusion in the field of measurement of I-E by getting away from the general undifferentiated concept of I-E. An inventory was constructed to measure, not a general trait, but 3 types or phases of I-E which were clearly defined. By a simple technique of item analysis, 3 homogeneous and relatively independent I-E tests were developed. Each test seems to be sufficiently reliable for individual prediction. The demonstrated ability of each test to discriminate between groups of college students which one would logically expect to be characteristically different in a given type of I-E justifies the conclusion that each test is sufficiently valid for the inventory to be employed in the diagnosis and counseling of college students.