career as a hospital administrator (classified as SER). Congruence
has been calculated using first-letter codes, three-letter codes, and
six-letter codes but requires the use of one of several mathematical
indexes (Brown & Gore, 1994; Camp & Chartrand, 1992) of the
degree of fit between the code of the person and the code of the
environment.
Consistency. Consistency is a measure of the internal coher-
ence of an individual’s type scores. Consistency is calculated by
examining the position of the first two letters of the three-letter
code on the hexagon. The closer the position, the more consistent
the code and individual. Types that are adjacent to each other on
the perimeter of the hexagon (for example, Realistic and Inves-
tigative) are more common and, therefore, harmonious than types
that are opposite each other on the perimeter of the hexagon (for
example, Enterprising and Investigative). An individual with an
I-E type might experience a chronic discomfort or “dis-ease” be-
tween Enterprising and Investigative interests, which are not often
found together and require nearly mutually exclusive repertoires of
behavior.
Differentiation. Differentiation is a measure of the crystalliza-
tion of interests and provides information about the relative defin-
ition of types in an individual’s profile. Typically, differentiation is
defined as the highest minus the lowest score among the six types
or among the three scores making up the three-letter code. The
highest differentiation possible would be a high level of resem-
blance to one type alone, whereas the lowest would be a perfectly
flat profile with identical scores on all six types. As Holland indi-
cates: “My purpose was to create a concept that would capture what
clinicians mean by a well-defined profile” (Holland, 1997, p. 26).
Identity. Identity is an indicator of the degree of clarity of the
“picture of one’s goals, interests and talents” (Holland, 1997, p. 5).
Identity is related to differentiation and consistency in defining the
strength of personalities and environments. Measurement of identity
is done with the Vocational Identity (VI) scale from My Vocational
Situation (Holland, Gottfredson, & Power, 1980). A comprehensive
384 CAREER CHOICE AND DEVELOPMENT