People are not black or white, nor are they red, yellow, green or blue

People are not black or white, nor are they red, yellow, green or blue? People have many things in common, but of course there are also countless individual differences between people. Two ways we can think about these individual differences are dimensional thinking and categorical thinking. The dimensional way means that you look at a number of dimensions in which people can differ and then look at individual how they score on each of those dimensions. The categorical way means that you define a number of categories and then look at each individual to determine to which category they belong. 

Categorical vs Dimensional 

Both approaches have their advantages and dangers. The dimensional way has the advantage that you can look at individuals in a detailed, fine-grained way. A danger or limitation of scoring people on dimensions may be that the dimensions you choose may not be relevant to the purpose for which you are making the assessment. Another possible disadvantage may be that assessing individuals on dimensions can induce a fixed mindset in those individuals. 
The categorical way of mapping individual differences has the advantage that it is nice and clear and simple. For certain types of decisions, it can be useful to divide people into categories (for example, who should be eligible for a vaccination and when?). But working categorically also has obvious disadvantages and risks. Putting people in boxes is often unnecessary and unfair. You reduce the individual to one characteristic. Moreover, it is often illogical to categorize people. 

Categorical thinking is popular 

We sometimes see this in discussions about 'black' and 'white' people. Skin colors come in a variety of shades. By pretending that you only have black and white people, you distort reality. (Ironically, black and white, the extremes of this continuum of skin colors, don't exist in reality at all!). Nor do we do this with human characteristics such as height, weight, age, intelligence, etc. In organizations, thinking about individual differences in a categorical way is more popular than I would like. This has to do with the simplicity and clarity that it appears to bring. But its relevance and realism usually fall short. 


I regularly hear people talking about a questionnaire called DISC. This questionnaire is based on a model by one William Moulton Marston in which people are scored on 2 dimensions (task-oriented/people-oriented and introverted/extroverted) based on which they end up in one of the following four quadrants: D (Dominating, Decisive & Direct), I (Influencer, Inspiring & Interactive), S (Stable, Social & Supportive), C (Conscientious, Correct & Calculating). These four types are indicated by the colors red, yellow, green or blue respectively. In order to communicate with or convince someone, it would be important to estimate which quadrant someone is in. The DISC approach is popular. It is written about in popular magazines and in successful books like Surrounded by idiots by Swedish author Thomas Erikson. 
This approach to psychology is simple and therefore attractive but unfortunately simplistic and therefore unusable and potentially harmful. Reducing people to "you are blue" or "you are red" is not realistic and does not do people justice. Little research has been done into DISC. There is therefore little empirical support for this instrument. In this article, the Swedish psychologist Dan Katz explains in firm terms what is wrong with (the approach of) Thomas Erikson and with DISC. 


Humans are complex and psychology is complex. I understand the temptation to make things simple. I therefore understand to a certain extent the attractiveness of black-and-white thinking and of questionnaires such as the DISC. But we shouldn't make things simpler than they are. In the end, we are all not served by that. It is best to exercise restraint and caution in thinking categorically about people. People are not black or white, nor are they red, yellow, green or blue.