You can find many versions of assessments based on Marston's DISC theory and several of them use graphs to help with interpretation. Some of these offer what they call natural, external, public, work mask, private, core, mirror, or adaptive styles. Even the old DiSC Classic had graphs I, II, and III, although DiSC Classic 2.0 uses only Graph III.
Why do people think there is an external or adaptive style?
Blame it on Walter Clarke, John Geier, or even William Marston himself. Marston theorized upon the difference between the public and private self. Early developers of assessments based on Marston's DISC model attempted to measure such a difference.
Does research support measuring an internal and external style?
No. That is why such a graph was removed from DiSC Classic and never part of Everything DiSC profiles.
As reported in the research report from Wiley, DiSC® Theory
The roots of the issue are sometimes traced to Walter Clarke, an industrial psychologist from the middle of the last century, who was among the first to design a personality assessment influenced by Marston’s work. His instrument, the Activity Vector Analysis, required respondents to answer a questionnaire twice. The first time, Clarke had respondents identify “words I have heard others use to describe me.” The second time, he had them identify “words I honestly believe describe me.” It is important to note that Clarke actually gave two separate instructions to respondents, so it was natural to presume that different concepts were being measured. Finally, we note that we have never been able to determine that Clarke did any further validation for this instrument.
Then, in the 1970s, John Geier, a researcher at the University of Minnesota, authored the first Personal Profile System® (the earliest version of DiSC Classic) building on the work of Marston, Clarke, and Cleaver. The PPS called for interpreting Graphs I and II as measurements of the public and private selves, respectively.
Indeed, it seems that the difference between the public and private self is among the richest of Marston’s concepts. In fact, much of the power of Marston’s theories may lie in this construct, and a better understanding of it may allow us to gain insight into behavior, adaptability, and other vital aspects of communication so central to DiSC. But Marston never designed an instrument to measure private and public self-perceptions; nor did he design an instrument to measure the “D,” “i,” “S,” and “C” emotions.
Still, his emphasis on the distinction between the public and private self may have influenced the researchers who attempted to harness this concept over the next 40 years. It may also explain why some practitioners have found the discussion of public vs. private selves such a compelling way to present deeper insights to users of DiSC.
Meanwhile, the fact remains that efforts to validate measurement of these separate parts of one’s self in an instrument have not been successful from a research perspective. In essence, there has never been well-documented support that any of the graphs are indicators of the private, public, natural, or pressured self or that they are anything other than measurements of general self-concept.
CURRENT RESEARCH ON THE GRAPHS
Wiley performed two preliminary studies to explore the validity of the alternative interpretations given to Graphs I and II. In Study 1, 376 people who had completed DiSC® Classic 2.0 also responded to 20 DiSC adjectives. They were instructed to rate themselves on these adjectives as others see them. These adjective ratings were used to create “D,” “i,” “S,” and “C” scale scores that reflected the individual’s “social” self-concept. These rating scale scores were then correlated with the DiSC Classic 2.0 forced-choice scale scores from Graph I, Graph II, and Graph III. It was hypothesized that if Graph I does, in fact, measure the public self, then the rating scales scores should correlate more highly with Graph I scale scores than with Graph II or Graph III scale scores. The opposite, however, was found. All four rating scale scores (i.e., our “social” self measure) correlated most highly with Graph III. Further, the median correlation with the Graph II scales was meaningfully higher than the median correlation with the Graph I scales.
In Study 2, 534 people completed DiSC Classic 2.0 and responded to the 20 DiSC adjectives mentioned above. In this study, however, after participants completed DiSC Classic 2.0, they were asked to recall a recent period of time in which they were under a great deal of pressure at work. They were then instructed to rate how well each of the 20 adjectives described them during that period of pressure. These adjective ratings were used to create “D,” “i,” “S,” and “C” scale scores that reflected the individual’s DiSC style under pressure. These rating scale scores were then correlated with the DiSC Classic 2.0 forced-choice scale scores from Graph I, Graph II, and Graph III. It was hypothesized that if Graph II does, in fact, measure the behavior under pressure, then the rating scales scores should correlate more highly with Graph II scale scores than with Graph I or Graph III scale scores. Again, this hypothesis was not supported. All four rating scale scores (i.e., our “pressured behavior” measure) correlated most highly with Graph III. In addition, the median correlation with the Graph II scales was only fractionally higher than the median correlation with the Graph I scales.
If you want a well-researched, accurate, and meaningful assessment, we recommend using Everything DiSC.