The history of DiSC measurement begins in the 1940s with an industrial psychologist by the name of Walter V. Clarke. Clarke built a test for use in personnel selection called the Activity Vector Analysis. He didn’t intentionally set out to build an instrument based on the DiSC theory, as his approach was almost purely empirical (i.e., letting the data speak for itself) rather than theoretical (i.e., looking for something specific in the data). Following the “lexical approach” that was popular at that time, Clarke identified a list of adjectives that were commonly used in describing others. He collected information on the adjectives using a checklist format, on which people are asked to check the specific words that describe them. After collecting and analysing the data on this instrument, he discovered that the four factors produced from the data (aggressive, sociable, stable, and avoidant) sounded a lot like DiSC. Clarke concluded that the data could be best explained by Marston’s model of human behaviour.
He scored the instrument in the following manner. He asked participants to complete the checklist twice, the first time responding by checking “any words I have heard others use to describe me,” and the second time responding by checking “any words that I feel honestly describe me.” The scores on the four scales, measured twice, were integrated into a single score for each scale (“composite self”), then ipsatized and plotted as a profile. The distance between the highest and lowest plotting points was divided into nine equal intervals regardless of the actual distance between the points. A segment number from 1 to 9 was assigned to each scale. The four-digit segment scores were then plotted as clusters in three-dimensional space, where distance between the clusters represented a measure of similarity. The clusters that came closest to each other were grouped into a mega-cluster (or pattern). Fifteen such mega-clusters (or patterns) emerged. It was these 15 basic patterns that formed the basis for interpretation of scores.