What is strong interest inventory (SII)?

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The Strong Interest Inventory (SII) is one of the most empirically sound interest surveys. The survey is relatively easy to administer and requires at least a sixth-grade reading level and a computer for scoring. There are twenty-three basic occupational scales, and the results are mainly applicable for use by people who are oriented toward professional, semiprofessional, or managerial occupations that attract college students.
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The Strong Interest Inventory (SII), which replaced the well-known Strong-Campbell Interest Inventory in 1985, was developed based on several decades of compiling empirical data. The empirical nature of the studies developed by E. K. Strong, Jr., is grounded in his observation of the specific interest patterns of workers in the occupational groups and careers he studied. He suggested that an individual who has interests that are similar to those of persons working in a given occupation is more likely to find satisfaction in that particular occupation than is a person who does not have common interests with those workers.

The SII contains 325 test items that measure a respondent’s interests in a wide range of occupations, occupational activities, hobbies, leisure activities, school subjects, and types of people. Most test takers can complete the interest inventory in about thirty minutes; the reading level is sixth grade. The survey is appropriate for use by people with an approximate age range of thirteen years through adulthood. The SII has been translated into several foreign languages for administration.

The scores can also be converted to a common reporting system developed by John L. Holland relating to a general occupational grouping or a job choice. The Holland system consists of six concepts arranged in a hexagon indicating relative positioning. The nomenclature for the Holland system consists of Realistic (R), Investigative (I), Artistic (A), Social (S), Enterprising (E), and Conventional (C) (also referred to as the R-I-A-S-E-C sequence).

Technical Aspects

The SII has been well researched in relation to other inventories by Strong and others. The stability of the SII is well documented, and reliability and validity studies suggest that the SII is well suited for career development, counseling, and review. Its validity and reliability have been shown to be reasonably consistent across a number of different cultures and ethnic groups. The strength of the SII is the variety of data generated on an interpretive report. This is useful in providing information that is usually not found on interest inventory profiles.

Interpreting the SII develops from a review of the general occupational theme scores. These provide three phases of review from the scores: first, a general overview of interest patterns; second, specific basic interest scores; and third, interests in specific occupations or jobs. The SII profiles are structured around Holland’s six occupational styles. Each of the six themes is reported and indicates whether the interest level is considered very low, low, average, high, or very high.

The basic interest scales focus on subdivisions of the six occupational themes from which career groups or clusters of occupations can be derived. Ten administrative indices are reported on the SII, including an infrequent response index, an academic comfort scale indicating the degree to which a person likes academic work, and an introversion-extroversion (IE) index indicating whether a person likes working with people or things. To make maximum use of the information on the SII profile, a systematic evaluation by a professional who can develop a complete evaluation of the responses is recommended.


Needs and interests have been found to be closely related. The relationship between needs, occupational interests, and personality identification has been demonstrated carefully. Holland’s research has also demonstrated that inner-directed and other-directed personalities differ in their occupational interests, as do people who are decided and undecided. The relative importance of interests to vocational decisions has also been extensively studied. Certain occupations evidently satisfy specific needs, and these needs are related to interests. With respect to career maturity, high scores on the SII correspond to other career inventory scores.

To make maximum use of the information on the SII profile, a systematic evaluation is recommended. For these purposes, an SII summary evaluation is devised from the total number of responses. Several steps are outlined for evaluation of SII scores along with the available interpretations.

For individuals to enter an appropriate career, they must begin to identify specific interests and relative importance of those interests. Some individuals will need little guidance in making career choices; others will need to guidance of a survey instrument such as the SII. Millions of people have received important information from it to use in decision making. Caution is always expressed by the authors of these inventories that no decision should be made solely on the basis of the results determined by one inventory alone. The SII is one of eighty interest inventories in use.


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