The Strong Interest Inventory (SII®) is a career evaluation model that aims to help individuals identify which careers they are most well-suited for, based on the individual’s self-reported areas of interest.
Sometimes known as “RIASEC” for short, the model stands for its six overarching career themes: Realistic (R), Investigative (I), Artistic (A), Social (S), Enterprising (E), and Conventional (C)—the Holland Codes.
The questionnaire typically takes 35–40 minutes to complete, and is administered and copyrighted by the Myers-Briggs Company. The model itself has undergone over 80 years of research and testing.
The Strong Interest Inventory is strictly an assessment of career interests (not aptitudes nor personality) and consists of 291 multiple-choice items with the five options: Strongly Like, Like, Indifferent, Dislike, Strongly Dislike. There are 30 professional fields and 260 specific jobs measured within the highly regulated psychometric assessment, written at a ninth-grade reading level.
The inventory is broken down into four key scales that have both psychometrically valid and reliable inter-scale correlations: (1) General Occupational Themes (GOTs); (2) Basic Interest Scales (BISs); (3) Occupational Scales (OSs); (4) Personal Style Scales (PSSs).
This comprehensive guide will take you through the questions (see also right side panel):
- What is the history behind the Strong Interest Inventory?
- Who is the Strong Interest Inventory for?
- How can you take the Strong Interest Inventory?
- How much does the Strong Interest Inventory cost?
- What types of questions does the Strong Interest Inventory ask?
- What does the Strong Interest Inventory measure?
- What report do you get with your results?
- How reliable and valid is the Strong Interest Inventory?
- How does the Strong Interest Inventory compare with other career assessments?
What is the History Behind the Strong Interest Inventory?
The Strong Interest Inventory was first developed in 1927 by psychologist Edward Kellog Strong Jr., who created the test during WWI to aid the military in finding jobs. He created the Strong Vocational Interest Bank (SVIB) to account for the post-war industrial boom and America’s growing vocational needs.
Dr. John Holland revised the SII® in 1974 to include the Holland Codes (RIASEC), to account for six different career themes (resulting in 720 code combinations!) that correlate with varying vocational interests:
- Realistic (R): Physical Strength, Hands-On Work, Machinery, Repairs
- Investigative (I): Research, Forensics, Analysis, Theoretical Thinking
- Artistic (A): Creative Writing, Photography, Film Editing, Sculpting
- Social (S): Teaching, Caregiving, Counseling, Coaching, Nursing
- Enterprising (E): Leadership, Selling, Managing, Entrepreneurship
- Conventional (C): Organizing, Finance, Bookkeeping, Law
More modifications of the Strong Interest Inventory were completed by Jo-Ida Hansen, Professor of Counseling Psychology at the University of Minnesota; and David P. Campbell, Professor of Psychology at the University of Minnesota.
Hansen served as an Editor for the Journal of Counseling Psychology, and Director of the Center for Interest Measurement Research. Both parties worked together to form the previous version of the SII, known as the Strong-Campbell Interest Inventory.
Who Is the Strong Interest Inventory For?
Anyone 13 years of age or older from the date of the assessment. For individuals younger than 18 years of age, career counsellors typically administer the Strong Interest Inventory® College and Skills Confidence Inventory to better assess their age-specific career needs. It is not advisable to administer the questionnaire to anyone under the age of 13, as they are still developing their interests.
The questionnaire can be used for career transitions, pre-employment interests testing, and career guidance for new graduates or emerging professionals in the workplace. It can be taken anywhere in the world as a fully virtual questionnaire, and is currently offered in both English and French.
How Can You Take the Strong Interest Inventory?
You can take the it online through a portal or mail-in your results to a designated branch. The entire assessment takes around 35-40 minutes to complete, on average. There are also licensed translators available to assist you if your primary language is not English or French.
If you select the online option, you can complete the questionnaire on your computer and results will be mailed to your inbox within 24 hours. If you select the mail-in option and fill out your selections with pencil, your results will take longer to process—from a few weeks to a month. Shipping times may also vary by country—anticipate delays by standard mail.
How Much Does the Strong Interest Inventory Cost?
Currently, as of 2021, there are four available officially licensed versions costs are as follows (before taxes) on the official Myers-Briggs company site (in USD):
- Strong Interest Inventory® and Skills Confidence Inventory Profile Administration®: $13.25
- Strong Interest Inventory® College and Skills Confidence Inventory Profile Administration®: $13.25
- Strong Interest Inventory® and Skills Confidence Inventory Profile + Strong Interpretive Report®: $20.25
- Strong Interest Inventory® College and Skills Confidence Inventory + Strong Interpretive Report Administration®: $20.25
Please note: only qualified and licensed practitioners and/or professionals who hold the BPS Test User: Occupational, Ability qualification (formerly known as Level A) are allowed to administer the test—and the prices listed above do not include additional interpretation costs from each individual practitioner or organization.
Great news: Many colleges and universities offer administration of the SII® for no additional charge, or a reduced fee—talk to your career counsellor for more information.
What Types of Questions Does the Assessment Ask?
The assessment begins by asking a series of 282 job scenarios (e.g. “Working with heavy machinery” or “Working with abstract ideas”) to which there are five possible choices: Strongly Like, Like, Indifferent, Dislike, Strongly Dislike.
The last 9 questions to add up to a total of 291 fall under the Your Characteristics subsection, with options: Strongly Like Me, Like Me, Don’t Know, Unlike Me, and Strongly Unlike Me. Here’s a breakdown of the areas the Strong Interest Inventory asks about with the number of questions:
- Occupations → 107
- Activities → 85
- Subject Areas → 46
- Leisure Activities → 28
- People → 16
- Your Characteristics → 9
These responses are weighed upon a standard Likert scale, with statistical scoring specifications: (Strongly Dislike = -2; Dislike = -1; Indifferent = 0; Like = +1; Strongly Like = +2). The higher the final total normal score, the more likely an individual is to succeed in a particular career sphere.
What Does the Strong Interest Inventory Measure?
The Strong Interest Inventory measures career interests and workplace preferences. Your answers reflect the type of work you’ll likely be most suited towards. Your answers are scored with respect to the Holland Codes “RIASEC” to determine your General Occupational Themes (GOTs), which further correlate with various individual career suggestions.
You’ll learn what interests you, how you’d like to work, and who you’d be most comfortable working with (small groups, large teams, etc.). The Strong Interest Inventory also scores your normal score matches to a database of 260 careers, and ranks them accordingly to give you a breakdown of your best-suited occupations and vocations.
Normal scores are gender-matched against one of two General Representative Sample (GRS) pool (i.e. male or female), that consists of 2,250 people (50:50 gender ratio).
The mean of the GRS is 50 and standard deviation is 10 (x̅ = 50, s = 10). All four Strong Interest Inventory scales reflect upon the GRS to breakdown percentages of careers and preferences according to gender.
The GOTs and BISs are homogenous scales, whereas the OSs are heterogeneous. Over half of people who take the SII receive different results for their GOTs and BISs compared to their OSs.
Note: OSs are based upon how specific people (either male or female) in a particular career tended to answer the questionnaire. Thus, it is entirely possible to have interests in art, but answer in a dissimilar manner from a painter, for example.
What Report Do You Get With Your Results?
Depending on the type of assessment you complete, you may receive a basic report of your Holland Code(s), or a more comprehensive breakdown of your exact percentages towards each of the six “RIASEC” career spheres. Again, the acronym stands for Realistic (R), Investigative (I), Artistic (A), Social (S), Enterprising (E), and Conventional (C).
The report breaks down your standard scores in General Occupational Themes (GOTs), Basic Interest Scales (BISs), Occupational Scales (OSs), and Personal Style Scales (PSSs). You’ll receive 10+ potential careers that may interest you and O*NET hyperlinks to learn more about their descriptions. O*NET components include Interests, Job Zones, and Careers.
For college students, the Strong Interpretive Report for Strong Interest Inventory® College and Skills Confidence Inventory includes a four-page supplement to the original nine pages that’s specially designed to guide the student and counsellor through school-related courses, extracurriculars, and majors that indicate potential vocational interests.
How Reliable and Valid is the Strong Interest Inventory?
According to the Myers-Briggs Company, the internal consistency reliabilities of individual scales are as follows (note: a statistically “perfect” score would be 1.0):
- General Occupational Themes (GOTs): 0.90–0.95
- Basic Interest Scales (BISs): 0.80–0.92
- Personal Style Scales (PSSs): 0.82–0.87
The mean correlation for the Occupational Scales (OSs) is >0.72, with an upper bound of >0.90. This makes the Strong Interest Inventory one of the most reliable and valid career assessments available.
According to the Myers-Briggs Company, the Strong Interest Inventory GOTs have been statistically “predictive of work-related variables,” “BISs can accurately distinguish occupations,” and the validity of PSSs have been shown to have relationships with both MBTI and the Skills Confidence Inventory. The OSs’ validity can be attributed to their excellent prediction of occupations people eventually enter.
How Does the Strong Interest Inventory Compare With Other Career Assessments?
The Strong Interest Inventory is seen as a leader in career assessments from school counsellors to job employment agencies. It’s often used in tandem with the Myers-Briggs Type Indicator (MBTI®)—which is primarily used as a personality assessment.
When both are used together, a career coach or counsellor can gain a better, more holistic view of an individual’s personality, behavior, and interests pertaining to their vocational interests.
Interestingly, sisters Katherine Cook and Isabel Briggs-Myers originally created the indicator as a best-fit assessment for jobs—which hit the corporate world by the mid-1950s. The sisters were self-taught students of psychology who used Jung’s theory of psychological types to develop their own assessment. The first rudimental version of the MBTI® was published in 1962 with the Educational Testing Service in New Jersey.
The DISC assessment, an open-source resource sometimes used in the workplace, is primarily used to indicate communication styles and encourage better teamwork within organizations. It’s split into four distinct communication categories: Dominant (D), Influencing (I), Steady (S), and Conscientious (C).
The Strong Interest Inventory, in contrast, aims to match people with their natural interests to encourage career satisfaction. This brings forth greater happiness and productivity overall—a win-win for every step of an organization—from recruitment to retainment!
At the end of the day, should you take the Strong Interest Inventory? We highly recommend the questionnaire to anyone who would like to find career direction or pivot into a new vocational realm.
References:
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.
Hansen, Jo‐Ida. (2010). Strong Interest Inventory. https://doi.org/10.1002/9780470479216.corpsy0950.
Hansen, J-I.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.
Holland, J. L. (1959). A theory of vocational choice. Journal of Counseling Psychology, 6, 35-45.
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.
Leierer, Stephen & Blackwell, Terry & Strohmer, Douglas & Thompson, Richard & Donnay, David. (2008). The Newly Revised Strong Interest Inventory. Rehabilitation Counseling Bulletin – REHABIL COUNS BULL. 51. 76-84. https://doi.org/10.1177/0034355207311342.
Strong, E. K., Jr. (1935). Predictive value of the Vocational Interest Test. Journal of Educational Psychology, 26, 332.
Strong Interest Inventory Manual (Donnay, D et al. CPP Inc., 2005).
Strong Interest Inventory Manual Supplement (Thompson, Richard, 2005, CPP Inc.).
