290 A
SSESSMENT AND
O
CCUPATIONAL
I
NFORMATION
The 25 Basic Interest scales (BIS) represent the next level of specificity, and
scores on these scales help the client to answer the question, “What do I like?”
They include scales such as Mechanical Activities, Sales, Medical Science, Ap-
plied Arts, Teaching, and Computer Activities. The BIS were developed using the
empirical method of clustering. As you would expect based on this method of
scale construction, the item content of each scale is homogeneous, with alpha co-
efficients ranging from 0.77 to 0.96. The test-retest correlations are large, with
medians of 0.85 and 0.80 over 30 days and three years, respectively (Harmon
et al., 1994). Similar to the GOT, evidence of validity for the BIS scores consists of
studies examining the extent to which the scales differentiate occupations in a
logical manner (e.g., auto dealers and life insurance agents score high, and psy-
chologists and physicists score low on the Sales BIS; Hansen & Campbell, 1985).
The Occupational scales provide the greatest level of specificity of interest
measurement on the SII and answer the question, “Who am I like?” They com-
pare the interests of the respondent directly to those of people employed in the
occupation who are satisfied with their work. A total of 109 occupations are rep-
resented on the profile; about one-third of the scales represent occupations that
typically can be entered without a college degree (e.g., carpenter, beautician,
florist, optician, travel agent), and the remainder represent occupations of a more
professional nature (e.g., architect, psychologist, nurse, marketing director, social
science teacher). The Occupational scales are arranged on the SII profile accord-
ing to their assigned Holland type (e.g., the Chemist scale and Biologist scale,
both coded Investigative, appear on the same section of the profile).
The Occupational scales are constructed using the empirical method of con-
trast groups. This technique identifies about 50 to 60 items for each Occupational
scale that differentiate the likes and dislikes of women or men in the occupation
from women in general or men in general. The item content of the Occupational
scales is heterogeneous; therefore, internal consistency measures of reliability are
not meaningful for Occupational scales. However, because the scales are used to
make decisions about college majors and careers, the concept of scale score stabil-
ity is very important for this set of scales. The median test-retest correlation for
the Occupational scales is 0.87 and 0.85, respectively, over 30-day and three-
month intervals (Harmon et al., 1994).
Evidence of validity for the Occupational scales was a major research focus of
early authors of the SII (e.g., D. P. Campbell, 1971; Hansen & Swanson, 1983;
Hansen & Tan, 1992; Strong, 1943). However, much of the evidence of validity for
the current version of the SII (Harmon et al., 1994) relies on generalizing from ear-
lier studies. Two studies (Savickas, Taber, & Spokane, 2002; Sullivan & Hansen, in
press) have demonstrated that the scores on the SII correlate substantially (conver-
g
ent validity) with scores on same-named scales on other interest inventories
(e.g., the CISS, the SDS, the KOIS, and the UNIACT). These same studies have
shown that SII scale scores have small correlations (discriminant validity) with
scores on other interest inventory scales that are unrelated. For example, the me-
dian correlation reported for same-named, scale scores for the SII and CISS was
0.62 and 0.66 for samples of women and men college students, respectively. For
the same sam
ples, the median correlations between nonmatching scales were 0.05
and 0.06 (Sullivan & Hansen, in press).
The extent to which the Occupational scales predict educational and occupa-
tional choices is a line of evidence of validity for SII scores that has been devel-
oped throughout the history of the inventory. The typical method for examining
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