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RehabMeasures Instrument

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The Strong Interest Inventory (SII), initially introduced in 1927 by E. K. Strong Jr., has become a well established instrument for measuring a person’s career interests.

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Instrument Details

Acronym SII

Assessment Type

Patient Reported Outcomes

Administration Mode

Paper & Pencil


Not Free

Actual Cost


Cost Description

Cost can vary; easy SII Interpretive report costs $15.95

Key Descriptions

  • 291 items that measure an individual’s interest in six areas, including:
    1) Occupations
    2) Subject areas
    3) Activities
    4) Leisure activities
    5) People
    6) Characteristics
  • For each of the items, the respondent is asked to indicate his or her preferences from among five response categories on an answer sheet.
  • The instrument uses a five-point Likert-type scale that asks people to answer by rating themselves from strongly like to strongly dislike.
  • The SII can be given either individually or as a group.

Number of Items


Equipment Required

  • Paper & Pencil for Standard Administration Computer
  • Keyboard
  • Mouse for Computerized Administration

Time to Administer

30-45 minutes

Required Training

Reading an Article/Manual

Age Ranges


18 - 64


Instrument Reviewers

Initially reviewed by Timothy P. Janikowski, PhD and his University at Buffalo Rehabilitation Counseling Master’s students, Allison Oste and Jessica West (4/11/2015).

ICF Domain


Measurement Domain



From the research done on the Strong Interest Inventory, it is a widely accepted measure for predicting future career opportunities based on the interests of the test taker. While it is a valid and reliable test, there is always the chance that the test taker will have some bias based on their opinions of what they are interested in and what they will succeed at doing. While the data suggests that based upon test takers results and their actual occupation or occupation that they foresee having, the test has excellent reliability and validity, the data does not take into account a bias within the test-taker, due to the self-report aspect of the test.

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Non-Specific Patient Population

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Standard Error of Measurement (SEM)

(Case & Blackwell, 2008)

  • Calculated SEM= 3.74

Normative Data

SII utilizes the General Representative Sample (GRS) for normative information, using an equal number of men and women, approximately 30% of whom are non-white. The GRS also consists of adults in 370 separate occupations (Donnay, Thompson, Morris & Sohaubhut, 2004).

Test/Retest Reliability

Population not established

(Kantamneni & Fouad, 2011)

  • Excellent: (ICC= .84-.89) 


(Case & Blackwell, 2008)

  • Excellent: (ICC= .86)

Internal Consistency

Population not established (Kantamneni & Fouad, 2011)

  • Excellent: (Cronbach's alpha= .90-.95)


Ultraorthodox Jewish Men (Pirutinksy, 2012)

  • Adequate to Excellent: Cronbach's alpha= .75-.95

Criterion Validity (Predictive/Concurrent)

Concurrent Validity:


Women (Gasser, Larson, & Borgen, 2007)

  • Excellent concurrent validity among women (r=.88) (Gasser, Larson, & Borgen, 2007)


Freshman Undergraduates (Female) (Hanson & Swanson, 1983)

  • 46.5% Excellent Direct Hit, 17.3% Moderate Direct Hit, 36.2% Poor Direct Hit Validity
  • 78.6% Excellent Indirect Hit, 3.6% Moderate Indirect Hit, 17.9% Poor Indirect Hit Validity


Freshman Undergraduates (Male) (Hanson & Swanson, 1983)

  • 39.5% Excellent Direct Hit, 21.0% Moderate Direct Hit, 39.5% Poor Direct Hit Validity
  • 87.9% Excellent Indirect Hit, 6.1% Moderate Indirect Hit, 6.1% Poor Indirect Hit Validity


Senior Undergraduates (Female) (Hanson & Swanson, 1983)

  • 57.1% Excellent Direct Hit, 16.2% Moderate Direct Hit, 26.7% Poor Direct Hit Validity
  • 71.4% Excellent Indirect Hit, 14.3% Moderate Indirect Hit, 14.3% Poor Indirect Hit Validity


Senior Undergraduates (Male) (Hanson & Swanson, 1983)

  • 59.3% Excellent Direct Hit, 16.3% Moderate Direct Hit, 24.4% Poor Direct Hit Validity
  • 77.1% Excellent Indirect Hit, 14.6% Moderate Indirect Hit, 8.3% Poor Indirect Hit Validity


Predictive Validity:

Female College Undergraduates (Hanson & Swanson, 1983)

  • 42.9% Excellent Direct Hit, 14.3% Moderate Direct Hit, 42.9% Poor Direct Hit Validity
  • 54.3% Excellent Indirect Hit, 14.3% Moderate Indirect Hit, 31.4% Poor Indirect Hit Validity


Male College Undergraduates (Hanson & Swanson, 1983)

  • 34.8% Excellent Direct Hit, 17.8% Moderate Direct Hit, 47.4% Poor Direct Hit Validity
  • 47.9% Excellent Indirect Hit, 22.9% Moderate Indirect Hit, 29.2% Poor Indirect Hit Validity

Face Validity

According to, the SII has Excellent Face Validity (2009).


Gender Bias Responsiveness ( Einarsdottir & Rounds, 2009)

  • Realistic scale (d=.85)
  • Investigative scale (d=.30)
  • Artistic scale (d= -.45)
  • Social scale (d= -.45)
  • Enterprising scale (d= -.09)
  • Conventional scale (d= -.24)


Case, J.C., & Blackwell, T.L. (2008). Review of Strong Interest Inventory®, Revised Edition. Rehabilitation Counseling Bulletin, 51(2), 122-126.

CPP. (2009). Validity of the strong interest inventory instrument. Retrieved from:

Dik, B. J., & Hansen, J. C. (2004). Development and validation of discriminant functions for the strong interest inventory. Journal of Vocational Behavior, 64(1), 182-197.

Donnay, D. A. C., Thompson, R. C., Morris, M. L., & Sohaubhut, N. A. (2004). Technical brief for the newly revised strong interest inventory assessment: Content, reliability, and validity. Retrieved from CPP website:

Einarsdóttir, S., & Rounds, J. (2009). Gender bias and construct validity in vocational interest measurement: Differential item functioning in the strong interest inventory. Journal of Vocational Behavior, 74(3), 295-307.

Fouad, N. A., & Mohler, C. J. (2004). Cultural validity of holland's theory and the strong interest inventory for five Racial/Ethnic groups. Journal of Career Assessment, 12(4), 423-439.

Gasser, C. E., Larson, L. M., & Borgen, F. H. (2007). Concurrent validity of the 2005 strong interest inventory: An examination of gender and major field of study. Journal of Career Assessment, 15(1), 23-43.

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(2), 194-201. 

Kantamneni, N., & Fouad, N. (2011). Structure of vocational interests for diverse groups on the 2005 strong interest inventory. Journal of Vocational Behavior, 78(2), 193-201.

Neukrug, E. S., & Fawcett, R. C. (2015). The essentials of testing and assessment: A practical guide to counselors, social workers, and psychologists. Stamford: Cengage Learning. 

Pirutinsky, S. (2013). Career assessment of ultraorthodox jewish men: Reliability, validity, and results of the strong interest inventory. Journal of Career Assessment, 21(2), 326-336.

Prince, Jeffrey P. (1998). Interpreting the Strong Interest Inventory: A case study. The Career Development Quarterly, 46(4) 339-346. 

Watkins, J.,C.Edward, & Campbell, V. L. (2012). Interpretation of the Strong Interest Inventory Testing and assessment in counseling practice. (pp 204-234). Hoboken: Taylor and Francis.