Note: If a cell is shaded, no Common Core State Standard is available for that domain at that grade level.

STANDARDIZATION AND PSYCHOMETRIC PROPERTIES OF THE WIAT-III

This section of the chapter describes the standardization sample and provides reliability and validity information for the WIAT-III.

142 ESSENTIALS OF KTEA™-3 AND WIAT®-III ASSESSMENT

Standardization

The WIAT-III was standardized with a grade-based sample of 2,775 examinees in pre-kindergarten through grade 12 and two age-based samples: 1,826 examinees ages 4 through 19 (overlaps with the grade-based sample), and 225 examinees ages 20 through 50. For each grade level, the sample size ranged from

150-200 examinees (with half of the examinees tested in the Fall and the other half in the Spring). For each age level, most sample sizes included 128 examinees, except age 4 with a sample size of 100, ages 17–19 with a sample size of 190, and ages 20–25, 26–35, and 36–50, each with a sample of 75.

The standardization sample was stratified to closely match the U.S. population. Thus, on the variables of gender, ethnicity, parental education, geographic region, and special education or gifted placement, the standardization sample closely corresponded to data from the American Community Survey of the U.S. Census Bureau for 2005 and 2008. The 2008 Census data were used for the adult norms, ages 20–50, which published in 2010; all other samples were stratified using the 2005 Census data. Self-education was used instead of parent education for examinees ages 26–50.

To establish a normative sample that 111111111is representative of the national school-age population, 4% of the normative sample consisted of examinees who met established criteria for a learning disorder in reading, writing, and/or mathematics; 1.9% of the sample consisted of examinees with expressive language disorder; and 1.8% of the sample included examinees with mild intellectual disability. A maximum of 1% of the sample at each grade level was permitted a diagnosis of attention-deficit/hyperactivity disorder (ADD/ADHD). In addition, 1.8% of the sample included examinees who qualified as academically gifted and talented. Separate norms are provided for fall, winter, and spring for grades Pre-K through 12, enabling the examiner greater precision by measuring an examinee’s performance against the normative sample at a specific semester of the school year.

Reliability

The internal-consistency and test-retest reliability coe cients for the WIAT-III are shown in Table 3.3 for subtests and composites. The average internal-consistency reliability values are in the .90s for the WIAT-III composite scores and for Math Problem Solving, Word Reading, Pseudoword Decoding, Numerical Operations, Oral Reading Fluency, Oral Reading Rate, and Spelling. The average reliability coe cients are predominantly in the .80s and .90s for Listening Comprehension, Early Reading Skills, Reading Comprehension, Sentence Composition, Essay Composition, Essay Composition: Grammar and Mechanics, Oral Expression, and the

WIAT®–III 143

Table 3.3 Average Grade-Based Reliability Coefficients for Subtests and Composites

Note: Subtest and composite reliability data are from Tables 3.1, 3.2, and 3.9 of the WIAT-III Technical Manual (Pearson, 2010a). Subtest component reliability data are from the WIAT-III Technical Report #2 (pearsonclinical.com). Mean grade-level values were calculated using Fisher’s z transformation.

144 ESSENTIALS OF KTEA™-3 AND WIAT®-III ASSESSMENT

Math Fluency subtests. Generally, reliabilities of .90 or higher support the use of a score for making educational decisions; however, scores with reliabilities between

.80 and .90 may also be suitable for educational decision making in some settings or circumstances.

As shown in Table 3.3, the WIAT-III subtest and composite scores possess adequate stability over time. Test-retest stability coe cients were used as the primary reliability estimates for subtests without item-level data (i.e., Essay Composition, Sentence Composition, Alphabet Writing Fluency, and Oral Reading Fluency) and subtests that are speeded (i.e., Alphabet Writing Fluency and Math Fluency subtests). The average corrected stability coe cients range from 0.87 to 0.96 for the composite scores, and most coe cients are in the .80s and .90s for subtest scores. The lowest average stability coe cient (0.69) is for Alphabet Writing Fluency due to the speeded nature of this subtest and the restricted raw score range.

In general, average test-retest gains are more pronounced for the Oral Language subtests (4–7 points) and the Reading Comprehension subtests (4 points) and are less pronounced for the Written Expression subtests (3–7 points) than for the other subtests. For the Written Expression subtests, the diminished performance of the second testing may be explained by the relatively greater amount of time and/or e ort involved in completing these subtests, which may lead to reduced motivation with subsequent testing sessions that follow closely in time.

111111111

Validity

The validity of the WIAT-III was demonstrated via multiple methods. First, intercorrelations between the subtests and composites were calculated to test for expected relationships and discriminant evidence of validity. Correlations with other instruments were also conducted to evaluate the construct validity of the test. Finally, special population studies were conducted to show the e cacy of applying the WIAT-III to the assessment of examinees with learning disabilities, language disorder, mild intellectual disability, and academic giftedness. The results of these special studies are detailed in the Clinical Applications chapter in this book.

The subtest intercorrelations confirm expected relations between the subtests within composites. The subtests that comprise each composite are generally moderately correlated with one another. Correlations among the composites range from 0.45 to 0.93, with stronger correlations among the Reading composites and weaker correlations between the Math Fluency composite and other composites. The intercorrelations also provide discriminant evidence of validity. For example, the Mathematics subtests correlate more highly with each other than with other subtests. Some examples of strong correlations across achievement domains are evident, such as the strong correlation between Word Reading and Spelling, which reflects the interrelatedness of some skills utilized across domains.

Correlations with other instruments were conducted to evaluate construct validity. Correlations with the WIAT-II suggest that the two instruments are measuring

WIAT®–III 145

similar constructs. The corrected correlations between the composite scores for the two instruments ranged from 0.76 (Oral Language) to 0.93 (Total Achievement), and correlations between the common subtests ranged from 0.62 (Oral Expression) to 0.86 (Spelling). Consistent with expectations, the corrected correlations were high (.80s) for subtests that are highly similar in con-

tent and structure to the WIAT-II subtests, but were lower (.40s to .60s) for subtests in which content and structure changed considerably, including Reading Comprehension (0.69), Listening Comprehension (0.64), Oral Expression (0.62), and the Written Expression measures: Sentence Composition (0.56), Essay Composition (0.45), and Essay Composition: Grammar and Mechanics (0.59). A summary of the WIAT-III correlational studies with the WIAT-II and KTEA-3 are provided in Table 3.4. Most correlations between like-named composites were in the .80s and

.90s, and correlations between the total achievement scores were in the .90s. Correlations between measures of oral language tend to be lower (.70s) due to greater content variations between measures.

When the WIAT-III was published 111111111in 2009, correlations were reported with the most recent version of the Wechsler scales at that time (WPPSI-III, WISC-IV, WAIS-IV, and WNV) and with the DAS-II. Since then, the WISC-V was published, and correlations between the WIAT-III and WISC-V were reported in the WISC-V manual. Correlations between the KABC-II and WIAT-III are not available. The correlations between the WIAT-III and the overall cognitive ability scores (full scale IQ [FSIQ] or general conceptual ability) from these measures range from 0.60 to 0.82. Generally, the WIAT-III core composites correlate highest with measures of crystallized ability and fluid reasoning.

Table 3.4 Correlations of WIAT-III With Other

Achievement Test Composites

Note: Data are from Table 3.11 in the WIAT-III Technical Manual

(Pearson, 2010a) and Table 2.11 of the KTEA-3 Technical & Interpretive Manual (Kaufman & Kaufman, 2014a). Sample sizes were N = 73 for the KTEA-3 study and N = 140 for the WIAT-II study.

146 ESSENTIALS OF KTEA™-3 AND WIAT®-III ASSESSMENT

Table 3.5 WIAT-III Composites Correlations With DAS-II and WISC-V Global Scales

Note: GCA = General Conceptual Ability; SNC = Special Nonverbal Composite; FSIQ = Full Scale Intelligence Quotient; NVI = Nonverbal Index. Data for the DAS-II

GCA are from Table J.1 of the WIAT-III Technical Manual (Pearson, 2010a). Data for the WISC-V are adapted from Table 5.13 of the WISC-V Technical and Interpretive Manual

(Wechsler, 2014b). Data for the DAS–II SNC were not published but requested post-publication (Jianjun Zhu, personal communication, May 16, 2011).

Table 3.5 shows correlations between the WIAT-III core composites and the overall cognitive ability and nonverbal index scores from the DAS-II and WISC-V. As expected, GCA and FSIQ scores correlate most strongly with the Total Achievement composite, and the nonverbal indexes from the DAS-II and WISC-V correlate most