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When considering psychometrics and neurosciences I asked Dr. Colin Wallace for some thoughts with supporting evidence.

The trait theory of personality suggests that people have certain basic traits and it is the
strength and intensity of those traits that account for personality differences. A trait is a
personality characteristic that meets three criteria:
(a) it must be consistent,
(b) it must be stable,
(c ) it must vary from person to person.
Based on this definition, a trait can be thought of as a relatively stable characteristic that
causes individuals to behave in certain ways.
For example:
(a) if they are talkative at home, they tend also to be talkative at work.
(b) at age 20 if someone is talkative they will also tend to be talkative at age 60
(c ) people differ from one another on the behaviours related to the trait. For
example, all people talk, but they differ on how frequently they talk.
If someone asked us to describe a close friend’s personality, what kind of things would we
say? A few things that perhaps might come to mind are descriptive terms such as “outgoing,”
“kind” and “even-tempered.” All of these are traits, but each one varies in terms of scale.
Myers-Briggs typology (MBTI) comprises sixteen trait ‘boxes’ (referred to as ‘type’) with
clearly-defined borders, but made no provision for scales or movement between them. In
other words, according to type theory, a person is born with a ‘type’ and retains that type
unchanged throughout their life. Really?
MBTI was based on four sets of binary (either/or) characteristics: extraversion vs.
introversion, intuitive vs. sensing, feeling vs. thinking, and judging vs. perceiving. Such a
structure is inherently weak because it excludes key information. For example, I am righthanded, but that does not mean that I cannot not use my left hand. My right hand is my
instinctive, preferred choice (natural behaviour), but I can also use my left hand when
appropriate, even though its use may be slightly less instinctive.
Another challenge to the trait approach to personality is that traits may not be as stable as we
think they are. When we say that “Nicola is friendly”, we mean that Nicola is friendly today
and will be friendly tomorrow and even next week. What we mean is that Nicola is friendlier
than average in all situations. But what if Nicola were found to behave in a friendly way with
her family members, but to be unfriendly with her work colleagues? That finding would clash
with the idea that traits are stable across time and situations.
Some of the most common criticisms of trait theory are based on the fact that traits are often
poor predictors of true behaviour. Even Carl Jung, whose 1921 book, ‘Psychological Type’
provided the basis for MBTI, admitted that these types were not absolute. “Every individual
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is an exception to the rule,” he said. For example, while an individual may score high on
assessments of a specific trait, they may not always behave that way in every situation.
Another problem is that trait theories do not address how or why individual differences in
personality develop or emerge.
The psychologist Walter Mischel (1968) reviewed the existing literature on traits and found
that there was only a relatively low correlation (about r = .30) between the traits that a person
expressed in one situation and those that they expressed in other situations.
Most important of all, the trait theory totally ignores the now well established fact of
‘neuroplsticity’ i.e. that human brain is in a process of constant change. As a person’s brain
changes physically throughout life, so does his or her behavioural responses.
The weakness of the trait concept was highlighted by Dr Ken Jennings, Director of the
Global Leadership in Healthcare Program at the University of Michigan Business School,
when he concluded:
“Fifty years of study has failed to produce a one personality trait or set qualities that
can be used to discriminate leaders and non leaders”.

[Jennings, E. (1961). The anatomy of leadership. Management of Personnel Quarterly, 11, 2.]

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