Standardization of the K-SNAP included a sample of 2,000 subjects ages 11 to 94 years, which was stratified within each of 13 age groups by gender, geographic region, socioeconomic status, and race/ethnic group. The K-SNAP standardization sample closely approximated 1988 U.S. Census data.
The mean split-half reliability coefficients were strong: .82-84 for the subtests (excluding Mental Status), .85 for the Recall/Closure Composite, and .89 for the K-SNAP Composite (see Table 15.5). Test-retest reliability was based on data from 132 normal adolescents and adults ages 11-91 years tested twice with an average test-retest of 30 days (see Table 15.5). Good test-retest reliability was found for the two composites (in the .80s), but the subtest reliabilities were mediocre, ranging from the mid-60s for Four-Letter Words to the high 70s for Number Recall and Gestalt Closure. Reliability for the Mental Status subtest was based on data from 54 subjects aged 55 or older, as this subtest is primarily intended for clinical populations and middle-aged or elderly populations; the mean stability coefficient was .74.
Results of factor analyses and age trend data provide excellent support for the construct validity for the K-SNAP. In a joint factor analysis of the K-SNAP, K-FAST, and KAIT (N = 1,270), clearly defined crystallized (Gc) and fluid (Gf) factors were identified in two-factor solutions (Kaufman & Kaufman, 1993). The K-SNAP Four-Letter Words subtest was associated with the Fluid factor, consistent with the notion that it measures higher-level reasoning and planning ability. And, as hypothesized, none of the K-SNAP subtests were closely associated with the Crystallized factor; that is sensible because the K-SNAP
tasks do not assess the types of tasks formally taught in school.
An additional factor-analytic study of the K-SNAP, K-FAST, KAIT, and WAIS-R produced a meaningful four-factor solution (Kaufman, Ishi-kuma, & Kaufman, 1994). The four factors produced by the sample of 225 were Gc, Gv/Gf (broad visualization and fluid abilities), Gf, and Gsm (Horn's short-term memory). The three K-SNAP subtests were each associated with different factors, with each substantial factor loading entirely consistently with the rationale for the K-SNAP's development: Four-Letter Words loaded on the Gf factor, Number Recall was associated with the Gsm factor, and Gestalt Closure loaded on the Gv/Gf factor. Thus, these factor-analytic studies suggest that the construct validity of the K-SNAP is supported by its relationship to the Horn constructs (fluid, broad visualization, and short-term memory).
The age-related patterns of performance on the K-SNAP also support its construct validity (Kaufman & Kaufman, 1994b; Kaufman, Kaufman, Chen, & Kaufman, 1996); these data are reported in Chapter 5.
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Whenever a doctor informs the parents that their child is suffering with Autism, the first & foremost question that is thrown over him is - How did it happen? How did my child get this disease? Well, there is no definite answer to what are the exact causes of Autism.