The Strong instrument measures interests in four main categories of scales: General Occupational Themes (GOTs), Basic Interest Scales (BISs), Personal Style Scales (PSSs) and Occupational Scales (OSs):
- 6 GOTs measure basic categories of occupational interests – Realistic, Investigative, Artistic, Social, Enterprising and Conventional (RIASEC) – based on John Holland’s theory (Holland, 1959).
- 30 BISs measure clusters of interest related to the GOTs in areas such as Athletics, Science, Performing Arts and Sales.
- 5 PSSs—Work Style, Learning Environment, Leadership Style, Risk Taking and Team Orientation – measure preferences for and comfort levels with styles of living and working. Personal Style Scales were added to the inventory in 1994.
- 260 OSs (130 for men, 130 for women) measure the extent to which a person’s interests are similar to the interests of people of the same gender working in 130 diverse occupations, such as Accountant, Bartender and Computer Programmer.
The current norm sample for the Strong is called the General Representative Sample (GRS) and consists of 2,250 individuals (50% men, 50% women). The GRS is generally representative of the racial and ethnic makeup of the U.S. workforce (Donnay, Morris, Schaubhut & Thompson, 2005). All scales are measured using the GRS, except the OSs (as described above).
Internal consistency reliabilities of all scales are high. GOT reliabilities range from .90 to .95, BISs from .80 to .92, and PSSs from .82 to .87. Determining internal consistency reliability is not appropriate for the OSs because the scales contain items with heterogeneous content and are empirically derived.
Extensive research has demonstrated the validity of the Strong Interest Inventory® instrument:
- Studies have found the GOTs to be predictive of work-related variables (Donnay & Borgen, 1996; Rottinghaus, Lindley, Green & Borgen, 2002).
- Research has shown the BISs can accurately distinguish occupations (Borgen & Lindley, 2003; Isaacs, Borgen, Donnay & Hansen, 1997; Larson & Borgen, 2002).
- Validity of the PSSs has been supported through research showing their relationships with the Skills Confidence Inventory (Tuel & Betz, 1998) and MBTI®instruments (Hammer & Kummerow, 1996).
- Validity of the OSs has been demonstrated in research showing their ability to predict the occupations that people will eventually enter (Strong, 1935, 1955; Campbell, 1966; Harmon, 1969; Hansen & Swanson, 1983; Dirk & Hansen, 2004).
- Borgen, F. H. & Lindley, L. D. (2003). Optimal functioning in interests, self-efficacy, and personality. In W. B. Walsh (Ed.), Counseling psychology and optimal human functioning (pp. 55-91). Hillsdale, NJ: Lawrence Erlbaum Press.
- Campbell, D. P. (1966). Occupations 10 years later of high school seniors with high scores on the SVIB life insurance salesman scale. Journal of Applied Psychology, 50, 369-372.
- Dirk, B. J. & Hansen, J. C. (2004, February). Development and validation of discriminant functions for the Strong Interest Inventory®. Journal of Vocational Behavior, 64 (1), 182-197.
- Donnay, D. A. C. & Borgen, F. H. (1996). Validity, structure, and content of the 1994 Strong Interest Inventory®. Journal of Counseling Psychology, 43, 275-291.
- Hammer, A. L. & Kummerow, J. K. (1996). Strong and MBTI® Career Development Guide (rev. ed.). Mountain View, CA: The Myers-Briggs Company, Inc.
- Hansen, J. C. & Swanson, J. L. (1983). Stability of interests and the predictive and concurrent validity of the 1981 Strong-Campbell Interest Inventory for college majors. Journal of Counseling Psychology, 30, 194-201.
- Harmon, L. W. (1969). The predictive power over 10 years of measured social service and scientific interests among college women. Journal of Applied Psychology, 53, 193-198.
- Holland, J. L. (1959). A theory of vocational choice. Journal of Counseling Psychology, 6, 35-45.
- Isaacs, J. Borgen, F. H., Donnay, D. A. C. & Hansen, T. A. (1997). Self-efficacy and interests: Relationships of Holland themes to college major. Poster presented at the annual meeting of the American Psychological Association, Chicago, IL.
- Larson, L. M. & Borgen, F. H. (2002). Convergence of vocational interests and personality: Examples in an adolescent gifted sample. Journal of Vocational Behavior, 60, 91-112.
- Rottinghaus, P. J., Lindley, L. D., Green, M. A. & Borgen, F. H. (2002). Educational aspirations: The contribution of personality, self-efficacy, and interests. Journal of Vocational Behavior, 61, 1-19.
- Strong, E. K., Jr. (1935). Predictive Value of the Vocational Interest Test. Journal of Educational Psychology, 26, 332.
- Strong, E. K., Jr. (1955). Vocational interests 18 years after college. Minneapolis: University of Minnesota Press.
- Tuel, B. D. & Betz, N. E. (1998). Relationships of career self-efficacy expectations to the Myers-Briggs Type Indicator® and the Personal Style Scales. Measurement and Evaluation in Counseling and Development, 31, 150-163.