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Wechsler Individual Achievement Test - 3rd Ed.

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by

Caroline Harris

on 22 February 2014

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Transcript of Wechsler Individual Achievement Test - 3rd Ed.

Wechsler Individual Achievement Test - 3rd Ed.
Validity of the Test
Inter-correlations range from .46 to .93 among the Language, Total Reading, Basic Reading, Reading Comprehension and Fluency, Written Expression Mathematics, and Math Fluency Composites.
Stronger correlations among reading composites between the Math Fluency composites and other composites.
Description of Normative Score
Evidence of Test - Retest Stability
Conclusion
WIAT-III

Is an academic achievement assessment used to measure knowledge in Reading, Writing, Math and Oral Language.
Scores are based on age norms and can be administered to individuals age 4 to 19.
Qualifications to administer: Individuals who have received professional training in educational or psychological assessment should interpret results of the assessment.
It contains 16 sub test.
Sources of Test Error
For sub-test with time limits, providing extra time invalidates the norms. A spoiled response, the student's elaboration reveals a fundamental misconception about the item, can reduce a score. Reading aloud the Oral Comprehension affects reliability of the subtest.
Uses of Limitations
Used

- to (a) identify the academic strengths and weakness of a student, (b) inform decisions regarding eligibility for educational services, placement, or a diagnosis of a specific learning disability, and (c) design instructional objectives and plan intervention.
Limitations
is - Even though the item content encompasses a wide range of skills and concepts, it was not designed as a measure of academic giftedness in older adolescents or adults.
Description of Normative Score - cont
Reliabillity of the Test
Reliability coeffecients for most of the WIAT-III sub-tests were obtained utilizing the split-half methods.
Writing Fluency, Sentence Composition, Essay Composition, Oral Expression, and Oral Reading Fluency do not have item-level data, and the Alphabet Writing Fluency and Math Fluency sub test are timed tests, test-retest stability coefficients were used as the reliability estimates for these sub tests.
Internal-consistency reliabilities are over .80, except for Listening Comprehension and Sentence Completion (.75 and .79 respectively).
Weighted Raw Scores
Reading Comprehension and Oral Reading Fluency, raw scores are first converted to weighted raw scores before being converted to standard scores.
Sub Test Standard Scores
Reading Comprehension and Oral Reading Fluency, raw scores are first converted to weighted raw scores before being converted to standard
Various moments (means, standard deviations, and skewness)of each score were calculated for each of the 28 (i.e., 14 for fall and 14 for spring) grade groups and 14 age groups of the normative samples.
Composite Score
To construct the composite score tables, sums of standard scores for each grade-appropriate composite were calculated for each student in the normative samples.
Growth Scale Value
Each subtest that has item scores in the WIAT-III, the raw scores were mapped to corresponding growth scale values using the Rasch IRT model (Rasch, 1960, 1961, 1966; Wright, 1968; Hambleton, Swaminathan, & Rogers, 1991)
Description of Standardization Procedure
Grade and Age Equivalent
Grade and age equivalents were constructed by plotting the median raw score for each grade or age and drawing a smooth curve through these points.





The WIAT-III was standardized on a national sample of 2,775 students.
Trained recruiters and independent examiners used various approaches (e.g., word-of mouth, referrals from other students, posting and distributing flyers) to identify students who met the specified inclusion criteria of the standardization samples and fit the sampling plan matrix.

The evidence of test-retest stability for subtest and composite scores was obtained by administering the WIAT-III twice.
Test-retest intervals ranged from 2-32 days, with a mean interval of 13 days for grades PK-5 and 14 days for grades 6-12.
Sources of Test Error
Standard Error of Measurement
The standard error of measurement (SEM) provides an estimate of the amount of error in an individual's observed test score.
The standard error of measurement is inversely related to the reliability; thus, as reliability increases, the SEM decreases, and confidence in the observed test score increases.
Student candidates for the normative sample were screened for exclusionary criteria that could possibly affect test performance.
Students with potentially confounding issues were excluded from participation.
A representative proportion of students from various special clinical groups were later added to the normative samples to accurately represent the student population as a whole.
Description of Standardization Procedure-cont
Description of Norm Group
Normative information was based on a sample representative of the U.S. population of students in grade PK-12.
Grade - The grade-based normative sample was split into a fall sample and a spring sample. The fall and spring samples included 1,400 and 1,375 students, respectively.
Age - The age-based normative sample included 1,826 student divided into 14 age groups: Age 4-13 were broken down into 4-month intervals; ages 14-16 were broken down into 1-year intervals; and ages 17-19 were combined into one interval.
Sex - The normative sample contained an equal or nearly equal number of female and male students in each grade and age group.
Race/Ethnicity - All Race/Ethnic groups were represented according to the general population distribution.
Education Level - Both normative samples were stratified according to the number of years of education completed by the students' parents.
Geographic Region - The United States was divided into the four major geographic regions: Northeast, Midwest, South, and West.
Strengths and Weaknesses
Strengths: If used with the Process Assessment of the Learner II it enhances the clinical utility by including more complete information about why a student is demonstrating poor learning outcomes and how best to intervene.

Weakness: The results obtained should never be interpreted in isolation, but in combination with a thorough evaluation and review of the students' history and background, culture, personality, current emotional functioning, and attention and motivational levels.
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