competencies; they culminate in a disposition or propensity to act
in certain predictable ways (repertoires). Types are measured using
interest items but are expressions of personality (Holland, 1997).
The six Holland personality types and their characteristics,
drawn from repeated empirical investigations of the correlates of
the types, are presented in Table 9.1. Work environments, accord-
ing to the theory, are characterized by the same six types. The theory
implies that many people resemble more than one, and in most cases all,
of the types to a degree. An individual’s personality is a composite of
all of the types; each individual has a unique combination. These
types reliably show characteristic repertoires of behavior and pat-
terns of likes and dislikes, hold specific values, and endorse unique
self-descriptions (Holland, 1997).
Subtypes. An individual may resemble one, two, or all six of the
Holland types. The pattern of scores and resemblance is called a
subtype. For example, a computer programmer might have a full
code of IRCA. Typically, however, the highest three letters of the
type code (IRC; called the three-letter code or summary code) are
used in assessment and intervention. The diagnostic signs describe
the relationships among types within a subtype or the relationship
between the subtype of an individual and the subtype of the envi-
ronment that individual inhabits.
The Hexagon and Diagnostic Signs. A detailed theoretical-
empirical calculus, or diagnostic system, has been logically derived
from the theory using the hexagon and is periodically undergoing
empirical test. An understanding of the indicators in this system
(congruence, consistency, differentiation, and identity) is essen-
tial to a complete understanding of Holland’s organizing system.
Congruence. Congruence taps the degree of fit between an indi-
vidual’s personality and the type of work environment in which he or
she currently resides or anticipates entering. An example of a highly
(though not completely) congruent person would be an individual
who had a three-letter code on the SDS of SEI and is considering a
380 CAREER CHOICE AND DEVELOPMENT