Insight Psychometrics Technical Manual - Canadian Test Centre

This is the fifth item plotted for the Gc subtest (the numbering here isarbitrary). As indicated in the title, this item was used in the finalassessment Levels 1 and 2. The Y-axis shows the difficulty (proportioncorrect) observed for the item for examinees of different ages (in years). Theplotting symbols indicate the test level, where 1, 2, and 3 are used for thelater development data and a, b, and c are used for the initial developmentdata. This item was used only in Level 1 for the initial development and inLevels 1 and 2 for the later development. It is an easy item and discriminatesby age within Level 1 and discriminates generally between Level 1 and 2. Forthis reason, it was included in both the Level 1 and Level 2 final test forms.Scale statisticsThe reported subtest and index scores for Insight are standardized scores(SS) and are age-normed. This implies that they each have an overalldistribution, within ages and across ages, with a mean of 100 and a standarddeviation of 15, as seen in Figure 16, which shows boxplots for each subtestand index.Figure 16: Distributions of standard scores for subtests and indicesStandard score distribution70 80 90 100 110 120 130Gc Gv Gsm Glr Gf Ga Gs IAS gI ITI IMPISubtest and summary scoresEach subtest is administered independently of the others and consists of it’sown set of items, but the subtests are correlated because the underlyingpsychological constructs are correlated. The summary scores (composite indexscores) are correlated highly with the subtests that compose them andcorrelated with one another because of the common subtests and also because15