This article by Paul F. Lazarsfeld and W. S. Robinson, originally published in 1940, addresses the methodological challenges associated with the use of case studies in psychology and social research. The authors critique the prevailing intuitive approach to classifying qualitative data, emphasizing its inherent subjectivity, lack of comparability, and limited precision. To overcome these limitations, they propose a systematic quantification procedure: case studies are classified along a predefined continuum using specific indicators identified within each case. Each indicator is assigned a numerical value reflecting its position on the continuum, and an aggregate score (typically the arithmetic mean) is calculated for each case. This procedure ensures greater objectivity, enhances comparability, allows for graded statistical analysis, and reduces classification variance. The authors illustrate the validity and practical utility of their method through its application in a study on the panic response to the 1938 “War of the Worlds” radio broadcast, demonstrating reliable discrimination of individual susceptibility to suggestion and establishing statistical relationships with educational attainment and behavioral outcomes. Lazarsfeld and Robinson conclude that their quantification approach holds broad applicability for researchers required to systematically classify case study or interview data.