(2) Differentiation. Some persons and/or environments can essentially represent one personality type rather than a mixture of types; these are clearly differentiated people or environments. Mixtures of many types are said to be undifferentiated or loosely defined.

(3) Identity. To the extent that a person or an environment has clarity with respect to goals, tasks, interest,s talents, rewards, etc., the person or environment may be said to have a stable identity.

(4) Congruence. To the extent that a person's personality type and the environmental type are the same, there is congruence between the individual's needs and the rewards supplied by the environment.

(5) Calculus. A single geographic model can be used to explain all relationships within and between personality types or environments.

From the foregoing assumptions and sub-assumptions, Holland derives a set of several conceptual principles. These can be delineated as follows: (a) Vocational interests and choices arise from personality type; (b) An assessment of a person's occupational interests is also an assessment of his or her personality type; (c) There are valid vocational stereotypes, e.g. the stereotype that actors are self-centered, that scientists have social difficulties, etc.; (d) Those who choose a particular vocation are similar in personality and in develo

The client characteristics included: gender, personality type (based on subjects' scores on the Vocational Preference Inventory), level of vocational identity and career decidedness, and degree of interest definition. The subjects were 102 individuals who sought assistance at a university-based career center.

Farrell, S.S. (1990). The differential effects of a computer-assisted and non computer assisted career/life decision program on the career decision skills of low-income women. Dissertation Abstracts International, 51(5-A), p. 1507.

However, Miller (1988) reported that with the introduction of Holland's theory, personality is now viewed as a valuable tool in explaining career interests and decisions. As a result, Miller states, there have been a number of studies which have attempted to investigate standardized personalty instruments for their validity as career guidance instruments, one of which is the Myers-Briggs Type Indicator (MBTI).

Miller, M.J. (1988). Integrating Holland's Typology with the Myers-Briggs Type Indicator: Implications for career counselors. Journal of Human Behavior and Learning, 5(2), 24-28.

Stein, T.S. (1991). Career exploration strategies for the elementary school counselor. Elementary School Guidance and Counseling, 26(2), 153-157.

Lenz, J.G., Reardon, R.C. & Sampson, J.P. (1993). Holland's theory and effective use of computer-assisted career guidance systems. Journal of Career Development, 19(4), 245-253.

The MBTI is an instrument designed to assess Jungian personality type. It does so by identifying four basic preferences: Extrave