The Strong Interest Inventory, published by CPP, Inc., and commonly referred to as the Strong, is one of the most widely used and scientifically grounded tools available for assessing people’s career and life interests.
The Strong measures an individual’s work and personal interests and compares them to those of people employed in a wide range of occupations. It is used to help people match their interests with compatible occupational, educational, and leisure pursuits. The 2004 edition of the Strong is the product of many years of research that began in 1927 with the research of E. K Strong, a military psychologist and an academician at Stanford University. The original Strong was titled the Strong Vocational Interest Blank (SVIB), and it consisted of occupational scales that were constructed through comparing item responses from individuals working in particular occupations with item responses of a general reference sample. The SVIB became the first formal interest inventory to be published. At that time, only male samples were used, and in 1933 the first Women’s Form of the SVIB was published. Eventually, in 1974, the Men’s and Women’s Forms were combined; Holland’s six dimensions were integrated to provide an organizing structure; and the name was changed to the Strong-Campbell Interest Inventory. Several revisions followed, resulting in additional scales and improved psychometrics. In the 1980s the name of the inventory was changed again, to the Strong Interest Inventory, which remains its current name. The Strong has been updated regularly to reflect changes in the culture of the U.S. workforce and to adapt to shifting career trends. It continues to be one of the leading inventories used by counselors in a variety of settings, including colleges, high schools, career development centers, and business organizations.
Administration and Interpretation
The Strong requires at least an eighth-grade reading level and fluency in English. It is not appropriate for individuals under the age of 13, and typically is not administered until an individual has reached the age of 16 or 17. The Strong assessment comprises six sections of items with a total of 291 items, each with a 5-point response option (strongly dislike, dislike, indifferent, like, and strongly like). Individuals’ responses are compared to a large general sample of working men and women (2,250 people) who generally are representative of the racial and ethnic diversity of the U.S. workforce.
Administration typically takes between 30 and 45 minutes. Individuals can complete the Strong online through the publisher’s SkillsOne Web site (www.skillsone.com) or manually using mail-in scoring forms. The resulting 9-page Strong Profile is sent to the counselor, not directly to the client. The publisher offers a number of tailored reports and Strong Profile options, such as the Strong College Profile, Strong High School Profile, and Interpretive Report, to tailor results to specific populations and needs. For example, the Strong College Profile provides a 4-page supplement to the profile to help both client and counselor connect the results to college majors, college courses, and campus activities that correspond to the client’s top interests.
Counselors need to demonstrate coursework in psychometrics or test interpretation (or to complete a workshop endorsed by the publisher) to qualify for ordering the Strong. The publisher offers a wide array of support materials to assist with interpretation. Both the manual and the several user’s guides offer detailed instruction for interpreting various types of profiles with individuals and groups.
The Strong Profile presents an individual’s interests through four sets of scales and uses John Holland’s theory of six vocational personality types as an organizing structure. The four sections include the following: the General Occupational Themes, the Basic Interest Scales, the Occupational Scales, and the Personal Style Scales. In addition, a number of administrative indexes are provided to help the counselor detect any unusual response patterns. An individual’s scores are compared to both men and women samples, but the majority of scores on the profile draw attention to comparisons with samples of the individual’s same gender.
The General Occupational Themes
The General Occupational Theme scales measure broad interest patterns used to describe an individual’s work personality. They comprise items with content corresponding to Holland’s description of the six occupational-personality types: Realistic, Investigative, Artistic, Social, Enterprising, and Conventional. Definitions of the themes are provided on the profile. Higher scores result from like and strongly like responses to items that relate to each of the six themes, and lower scores result from dislike and strongly dislike responses to these items. The six themes are presented in rank order of interest level on the individual’s profile using interpretive comments that compare the individual to a reference sample of the same gender. These comments range from very little to very high interest. Standard scores, which compare the individual to a reference sample of both genders, are then used to further rank-order any interpretive comments with similar values. Individuals are given a Summary Code that highlights the combination of the individuals’ highest scoring themes to encourage exploration of two or three themes rather than to one alone.
The Basic Interest Scales
Thirty Basic Interest Scales measure more focused interest areas using the same construction and scoring methods as the ones used for the General Occupational Themes. These scales, such as Culinary Arts, Law, and Office Management, are grouped on the profile according to the six themes. They can be used to break down the General Occupational Themes into specific interest areas related to work, school, or leisure activities that the individual is likely to find interesting and rewarding.
The Occupational Scales
The Occupational Scales include 122 scales that represent a wide range of occupations representing all six themes. These scales measure how similar an individual’s interests are to those of people of the same gender who have been satisfactorily employed in a particular occupation. Scores reflect a comparison of both the dislikes and the likes of an individual with the dislikes and likes of satisfied workers sampled from that occupation. Consequently, the higher the score, the more the individual shares similar interests and disinterests with people from that occupation. The profile highlights the 10 occupations most closely aligned with the individual’s interests, and scores are presented for each of the 211 scales using a bar graph that extends from dissimilar to similar. The profile shows only comparisons with samples of the individual’s same gender (unlike previous editions of the Strong, which included comparisons to both genders).
The Personal Style Scales
The five Personal Style Scales describe different ways of approaching work, learning, leadership, risk taking, and team participation. Unlike all other scales on the Strong, each of the Personal Style Scales is presented as a bipolar continuum and describes the individual’s preference for one style versus another in comparison to a reference group of men and women combined. Scores are labeled as clear when they fall toward either polarity of the continuum, and as midrange when they fall toward the middle. Descriptors are provided at each end of each continuum providing examples of a preference for one style versus the other. For example, the first Personal Style Scale, Work Style, describes scores toward the left pole as “Prefers working alone; enjoys data, ideas or things; reserved,” and scores toward the right pole as “Prefers working with people; enjoys helping others; outgoing.”
A summary page is provided on the last page of the profile. This page summarizes the individual’s highest themes, top five specific interest areas, top 10 occupations, and each Personal Style Scale preference. The areas of least interest to the individual also are summarized here. The purpose of this page is to help the individual focus on common interest themes that are consistent throughout the profile.
Research and Practice
The Strong is one of the most extensively researched inventories available. The developers engaged in significant research to support the current edition, and numerous scholars have published a large body of literature to support the instrument throughout its history. The Strong Interest Inventory Manual provides detailed descriptions of the research that led to item selection, scale construction, reference sample collection, and scoring. Evidence for both the validity and reliability for each set of scales on the Strong is impressive and provides strong support for confident use of the Strong with a variety of client populations. Used appropriately, it serves as a dependable tool for helping clients make informed career, academic, and life decisions.
- Donnay, D. A. C., Morris, M. I., Schaubhut, N. A., & Thompson, R. C. (2005). Strong Interest Inventory manual. Mountain View, CA: CPP.
- Grutter, J., & Hammer A. L. (2005). Strong Interest Inventory user’s guide. Mountain View, CA: CPP.
- Prince, J. P. (2007). Strong Interest Inventory college edition user’s guide. Mountain View, CA: CPP.
- Prince, J. P., & Heiser, L. J. (2000). Essentials of career interest assessment. New York: Wiley.